Welcome to the Team Bart!
Nice Shop. I'm envious to say the least. You are going to need one lift and possibly a swiveling boom crane depending upon how big and strong you are to move engines and other heavy chunks of iron around the shop.
I would separate car from frame and see if it can be saved buy cutting out the rot and welding in flat sections of eighth inch steel flat plate to replace what is cut out then box the frame in fully. You can run extra large solid fuel lines, and a return line inside the frame rails along with new stainless steel brake lines. Once fully welded and ground down you can everything powder coated all at the same time. That would look better, be as strong though a tad heavier than a full tube space frame.
Once boxed in and with plastic body bushings to tie the body to the frame you can run 1,200 horsepower through the combination. Of course finding tires to support that power level will require serious surgery to your rear quarters, a narrowed rear frame, and huge rolled sheet metal drums for inner fenders if you want to hook up. But with a well prepped track you can stand her on her back bumper (I've done it).
I recommend by-passing a search for a 12 bolt and ignore the nine inch as an option and go straight to a Dana 60 for a rear end. It is stronger than anything else you can find and doesn't have the parasitic drag of the nine inch.