More random thoughts. Please keep in mind I'm not a purist and have no problem with people swapping in 9" rears, 5-6 speed manuals, overdrive autos, Fuel injection, BBC's, SBC's, LS engines, Buick engines, Olds engines or any thing else including Coyote's. I'm a 2nd gen F body cheerleader! However in this case I think adding an LS/drive train swap would create an almost impossible project because you'd be dumping all of your time and money into the car for many, many, years with no driving enjoyment and that gets really old after 10-15 years.
Look at the two unfinished project cars you bought. Both were relatively small projects. 78 guy had the drag race dream. Doubt he ever made it to the track because the fuel pressure regulator mounted on the firewall is a huge red flag in tech inspection. 76 90's wheels guy had the early nose swap dream. We can see that didn't get finished. It's very easy to run out of time, money, stamina, desire, or have life get in the way of progress.
Taking two rusty 45 YO modified/hacked parts cars apart, selling off unneeded parts and building one roadworthy car out of them is a huge project by itself. HUGE!
Bodywork & paint on a 2nd gen Trans Am is a LOT of work compared to most of the popular cars of the era. There are a lot more parts that take a lot of time to remove, strip, repair, & prep & then paint separately and install. Even body shops often under estimate the work involved on these cars and frequently end up in trouble with unhappy customers because the current shop employees hadn't ever done one so original estimates were waaay too low. If a shop tells a 2nd gen TA owner they'll do basic prep & paint for 5 grand with no rust repair there's gonna be a problem.
More types and quantities of materials are necessary to do the body & paint work compared with other cars of the era. Soft plastic repair and hard plastic repair two part materials are needed in addition to regular bondo, primer, sealer, and paint. You'll use a lot more sandpaper, wax & grease remover, primer, thinner, tape, masking materials, and paint because of the losses spraying all the small parts along with the extra materials that end up staying on the parts.
Parts most cars of the era don't have or are different on a TA that require extra time & materials.
Three rear spoiler sections
Rear bumper cover
Four wheel well flares
Four wheel well flare welting strips
Four side running light bezels
Urethane nose/bumper cover
Front spoiler
Shaker scoop
Two fender air extractors
Two grills
Two tail light bezels
Four door mirror sections
Trunk filler panel isn't welded in like most cars so it has to be removed for paint.
Most people think "Pffft how much extra time could the pieces take?" so I suggest to pick just one small piece like a fender flare or an air extractor and make it ready to install. Sand all the crappy old paint materials off, repair any damage like cracks or missing chunks, fill nicks/chips & sand, prime, sand, seal, and then paint car color to see if they did a good job.
There's a reason there's sooooo many 2nd gen Trans Ams sitting disassembled in garages all over the country. It's a LOT more work than most people expect to do even for a DIY home garage driver quality repaint.