Leaking transmission

Are there any major changes needed for a V8 swap?
Well that depends if you're piecing it together, or if you have a donor-car, and what the end-goal is.
To piece it together, you would need the correct engine brackets and insulators, the exhaust manifolds and a new exhaust system. Then you need to hook up the carb so it and the kickdown all work properly, and cannot hang up, wide open. Then there's electrical,cooling and fuel to deal with. And an air filter system.
And after that, there's suspension steering and brakes to deal with, and probably a suregrip and tires. And seat belts I guess, cuz even a 273 will nearly double your power.