My first Car was a 57 Ford Custom Tudor (looking like a Fairlane 500 but was a post car, instead of a hardtop. bought it in 1965.
The car originally had an in-line 6 with a 3 speed manual and a small rear.
After driving it for a couple of years like that, I eventually swapped in a Ford 9" rear. it was a straight bolt in.
The next change was a was a Small block MoPar with an 833. Snug fit but manageable. The engine was basically a stock 273 ( a dime a dozen at the time) with a 625 AFB (vac. secondaries), and Edlebrock manifold. As I recall it was a "Streetmaster 318", and a set of Doug Thorley headers into Hush Thrush mufflers. Later I added an electronic ignition system from a wrecked early 70's MoPar.
The car not only got faster, with fantastic reliability, it also gained by leaps and bounds in driveability.
There were really only a few issues to over come: The motor mounts, the trans mounts, the drive shaft, and some steering column clearances.
My cousin Tommy fabricated a set of mounts in metal shop in high school with the help of the teacher (also a gear head) that worked the first time, with some GM biscuits. I drew up the modifications that needed to be dune to to the Ford trans mounts to support the 833. Involved adding some tabs to the tail end of the trans for stability, and we modified the headers by 7/8" (as I recall) to clear the steering column and box.
I bought the car for $25.00 in 1965. over the years that I owned it, I don't believe I spent more than about $2000.00 on it in total for mods, including the rear, the driveshaft mods, the motor and trans mounts fabrication, the 833, the 273, headers, intake, carb, air cleaner, and other mods like paint, and interior, and such.
Nearly everything (except paint) was done in my garage, at home, by me, my cousin, and friends, and I drove the car for some 8 years. It was my daily driver, and became my tow vehicle when I bought a new 68 Hemi roadrunner.
Flat towed at first, but later I added a helper leaf to the Ford's rear, and air bags (used to have to get under the car to add or release air from the bags), so I could trailer the Road Runner to Great Meadows, Atco, and E'town, and sometimes even to the old National Speedway on Long Island.
Have fun. Here are a couple of pics of the car I had (traded it for my Barracuda). 
