Since nobody else has gotten into it:
The good:
This car APPEARS to be a sport coupe. That was what a ttype was called before 1983. This means
* The hood ornament and 3 badges are worth about $150-$200 US. Value is higher if you swap the 1981 base for a 1984-87 base.
* from the factory you had a quick ratio steering box, 5 pod gauge cluster, and sport suspension spring/shock package.
This does NOT mean you got a 8.5 rear, those didn't start until 1984. It came with a plain 7.5, and, sounds like maybe gears were already swapped - if not you've got 3.42s, not necessarily posi.
If original still the steering wheel has value as a core or better based on condition.
Now, as a regal you've got better access to more reproduction parts than any other gbody due to grandnationals, followed closely by monte carlo ss.
The BAD:
That body is beyond saving in any economical manner, there's maybe a half dozen guys on this site that COULD save it, and, outside of them, to pay to fix it is probably a $40,000 to $50,000 investment. It's literally rotting from the inside out at this point, and, likely would be a thousand hours of labor or more. A pillars, hinge pillars, rockers, floors, roof, quarters- all going from inside out from those pics... and who knows about underneath the car or the firewall.
The transmission may be on its last legs if it was being run dry of fluid and getting damaged - and the ad says it'll run dry when driving so that probably means it's been dry.
With that level of transmission maintenance you have to question how well maintained any of the rest was either.
So I see a parts car body, thats been hacked up. I see MAYBE a core transmission that may have heat damaged internals which means it's really only a case at this point. I see a lump sbc that may not be anything special and is of dubious maintenance status.
I'd rather a car with rocker or floor rust than one that's rusting from the inside. Think about it... all that water runs inside the body, over untreated/unprotected inner metal carrying rust particles with it. These cars didn't have the level of corrosion protection they use now. All that rusty water went somewhere, starting new rust as it went.
If you do take the plunge then everyone here would do their best to help you out. But I think, especially given how you describe your tool/space/etc situation you're better off holding your money and waiting. 2 months and it's fall, people won't want to store summer toys for the winter and more inventory will come up.