Re: 366 carb to 427 FI swap!!
That 1995 427 is going to have TBI on it which is STUPID simple as far as fuel injection is concerned and there is a wealth of information on the subject. If ever there were a system that a newbie should dive into that would be it. I wouldn't be worried about the transmission either. An AT545 is the most likely transmission and it has nothing other than a detent cable to the best of my knowledge. An MT643 has lockup on the converter, but even then I believe it is just the detent cable that modulates it. If the original 427 ECU was supposed to control a transmission like a 4L80E it won't care if one isn't there.
Just some food for thought...I'm all about fuel injection where ever possible, but a carb might be easiest. Why are you swapping from the 366 in the first place? They are gutless, but the spread from the most gutless skoolie engine to the most powerful is not very wide. I wouldn't worry about reliability at 300,000 miles if it isn't giving warning signs like noise or high oil consumption. They are solid engines.