Having done this conversion, sort of, I can tell you that there are things which you have likely not imagined would have to be changed.
I bought a '65 that had its original 200 6cyl replaced with a 302. That's all they did. It still had the small drum brakes, the 7 1/4 integral rear end, 4-lug drums all the way around, the lighter front springs and everything else Ford used for the 6 cylinder Mustangs. So, while I did not do the engine swap I did everything else to make the car safe after the engine swap. I found an 8 inch rear end which gave me the 5-lug rear brake drums so that I could use 5-lug wheels. I converted the front spindles to a Granada set up so I could use 5-lug wheels on the front. That also gave me front disc brakes. I had to change my tie rod ends, steering idler arm, drag link, springs, master cylinder and brake lines. I figured that, while everything was apart, I should change sway bar end link bushings, strut rod bushings, upper and lower control arm bushings and put in heavier-duty front springs to support that heavier V8.
Go through a catalog and price all those things to get an idea of what it's probably going to cost.