Yeah its a bummer when you do the work install the engine only to find that it is blown. Just had that happen with a 4T60e transmission on my 4.9L. Guy who sold it to me swore that trans was in good shape. Then he skipped town and was never heard from again. Had to take everything out and start over. Its a real PITA and a downer but it happens. With all the work that you have done, I'm certain that you will get it right and have a nice replicar to drive. The only thing that I would additionally check is to see if the car (without the roof) has a sufficient extra sub frame to avoid body flex.
------------------ " THE BLACK PARALYZER"
-87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 09-13-2021).]