I did something similar (but lower-budget) back in the day.
The only car I've ever gotten for free was a 68 notchback/289/automatic.
It was driven about 100k miles and then garaged for a couple of years - this was 1972.
My best buddy wrapped his 66 Cyclone/390/335hp around a telephone pole.
He wasn't injured, but the car was totalled.
His father happened to own a transmission shop. So we had his car towed there, pulled the engine and trans (4 speed). Gave his dad the trans in exchange for a used short C6 with flywheel and went to get my car. - I'd have loved the 4 speed, but installing a clutch linkage in an automatic car, not so much :(. We managed to get the old 289 running, but just. Maybe a mile from the shop, the front U-joint broke and took the C4's tail shaft housing with it (I think I still have that part somewhere, I save weird **bleep** like that!) All I needed from the local Ford dealer was a set of big block motor mounts, and the correct drive shaft, not too expensive, I was on a tight budget being a student who worked weekends pumping gas. I SHOULD have changed the small-block rear end for a bigger one, but didn't have the money for that. Quick fix: remove the yolk from the diff and have the U-joint retaining notches machined off. Bigger U-joint now fits perfectly! Cobbled together a dual exhaust using parts from the Cyclone and got a big-block Mustang/Cougar radiator from a junkyard.
I kept the 289 badges on the side of the car and won lots of street races. 🙂
Sold it in 73 to raise money to buy a brand new 74 Dodge van!
PS: In the summer of 67, I met 2 kids in Santa Monica whose dad worked for Shelby. As Ford was closing down the CA operation and moving it to Michigan, their dad had his 67 GT500 (with 68 updates) for sale. It was light metallic blue, black interior and an automatic. I'll never forget the test drive dad and I took on the 10 freeway. We could have bought that car for..... wait for it..... $3000! But my mom said no. That woulda been my 1st car! 😞 The man's name was Grimm. If anyone knows the history of that car, I love to hear it.