NA in Portland OR area?

I'm assuming the boat will have a fairly distinctive "scum line" that shows where it has been floating.
With the boat at rest the CB and the CG are in the same lateral and longitudinal place, the difference being their positions in the vertical.
Total weight, (displacement,) is what it is, if the Travel lift is calibrated it'll give the weight.
An inclining experiment will determine some other things, but it is a lot of work, requiring completely calm conditions, and helpers generally needed.

 

I went out and took few pictures of the WL/scumline. It shows well.

 

Well it depends on what you're hoping for. Solving the issue or solving it cheap. I don't know your budget, so I can't say if you'll be able to afford the cure.

Here is the issue: the Roberts 53 hull was supposed to displace ~50 000 lbs, 17 000lbs of that beeing ballast placed at the bottom of a fin (original draft was 6'6"). Your hull has had the fin cut off just below the prop exit significantly reducing draft, ballast reduced to 6000 lbs plus the water tanks, and enough superstructure added to bring the displacement to 67 000lbs. To counter the additional weight and it's shift towards the stern a flotation blister was added, and the forefoot has been somewhat filled in with that I beam in front of what remains of the fin keel.
By doing this, the entire CG has migrated several feet up.

To fix the rolling issue you need to transform the underwater shape more to a hard chine type (fairing the boat from midship aft with hughe blisters) to pick up form stability, then ballast needs to be added as low as possible (this means using lead not concrete) to lower the CG significantly.
Between fees to the NA to measure the existing and design the modifications, building and installation cost and acquiring and shaping the ballast, you are looking at a relatively big chunck of cash.

 

I haven't asked the travel lift operator about the weighting option, but I really hope they can provide that.

I am still searching for the incline test person who could do it for me, but I am not sure how successful the search will be.
Meanwhile, I was looking at these guys doing it on a sailboat:
How to measure your yacht's stability - Yachting Monthly https://www.yachtingmonthly.com/gear/how-to-measure-your-yachts-stability-72953

 

I did not know that my boat had a ' fin '?
I know it had rolling chocks, but those were cut off. I have no idea why and when?
Is this Roberts 53 hull available to see on the web?
Maybe this one? It shows a fin at the end.
Roberts 53 Boat Plan | Boatbuilding & Designs https://www.finelineboatplans.com/bruce-roberts-53-boat-plan

 

What are those blisters look like?
Would the existing blister on the stern be part of it, or would that be cut off?

 

I will do a number of measurements while on dry, no matter how long it takes. I hope I can do a complete one side hull's lines plotting with 10-12" increments. I plan to use laser distance tool, tall tripod, plumb bob, levels.

 

The mark that waterline may have left on the hull doesn't necessarily have to be the current waterline. What needs to be known is the weight of the boat as it currently sits.
True, the CoB and CoG, with the boat in equilibrium, will be in the same longitudinal and transverse positions, we agree, but what does that have to do with the waterline CoG?
Inclining test, afloat or in the air, is the only way to reliably determine the CoG position. It's certainly a process that must be performed by experienced personnel and is expensive, but what are you proposing in return? That's the crux of the matter.

 

That's your boat in its original design as a sailboat. The grey block at the bottom end of the keel fin represents the 17 000lbs of ballast that was intended for her. Whoever had the bright ideea to convert her to a motorboat didn't like the 6'6" draft, so they removed most of the fin, keeping just enough to protect the prop. This stump now probably houses some ballast. It would have been relatively fine like that if the same chap hadn't built all that superstructure on top. Now the center of gravity is way up, and with her multichine sailboat hull there isn't much form stability to dampen rolling.

If you don't want to cut off everything that's higher then 2ft over the deck, you must add significant ballast, and in order to retain enough freeboard you need to add enough underwater volume to float that ballast. Anyway, nobody can tell how exactly the whole modification should look without a proper analysis of the boat as she is now. This includes an inclining test, and basically a complete redesign of the underwater shape. You will end up fabricating and welding on a new underwater hull around the existing one, and ballasting the result as a whole. That's why I said I have no ideea if you can afford to have this work done, this isn't a cheap fix like bolting on some additional weight.
The previous NA did what he could no doubt under the constraints imposed by the client, fix the excessive weight problem and trim her level.

 

Finally I understand my boat's behavior. Thank you for this explanation.
Yes, there is a lot to think about.....

 

Not really. It's so simple. Just not palatable. Sad really.. or not, just simple.

 

I am not giving up just yet. The thinking is about monetary needs for an acceptable solution. There are many ways to skin a cat....

 

What do you mean by underwater volume? Blisters, sponson, solid plates, hull alterations?

 

OP, finally after 3 pages some revealing info comes to light, (part of the boat is missing).
Rumars has hit the key point.
An old saying; "When you find yourself in a hole, quit digging".
Find someone who wants something to tie to the dock forever to live on it and sell it to them, then walk away.
Youth and idealism only last till the money runs out, then you're still in the hole only now it's deeper.

 

Same thing Ad Hoc told you in the other thread,
extend the lines straight back from the widest point of the hull, then create a new hull shape along those lines, with a new transom. That should give you a much wider underwater hull.
The big question is if it's enough volume for the amount of ballast you will need to lower the centre of gravity. Or even if your expectations can be met by a modification, even an extensive one.
It all can be answered beforehand by a NA, but it means he has to come out, measure the boat, do an inclining test, then use all that info to design the best compromise of hull volume and ballast placement. Otherwise you are again shooting in the dark, hoping to hit something.

Get quotes for all the work needed to be done, both by the NA and by a shipyard. You can then decide if it's cheap or expensive, and if it warrants doing at all. After all there's only so much anyone can do before its cheaper to build a new hull.

Lastly, it's your boat and you do what you want to it. If you want to start welding tomorrow doing it all by eye, that's fine by me.