You will get lots of opinions about engines and HP. I asked similar questions and was told 350 to 400HP is the sweetspot, and then you'll see other people with much more HP arguing that you can drive it as fast as you need.
I was convinced I was going to use the Ford Coyote engine but got scared off because of the technical side involving engine management etc. I suspect you are thinking of a big-block 427 like the originals. Big blocks my be detrimental to handling for sure which is probably why most builders here stick with small blocks. You can still get tons of HP from these and they are reasonably light. In the end I opted for a Ford 351W based 427 cubic inch engine pushing around 560HP. I don`t believe EFI will sound any different to a carb engine. As for transmissions - the Tremec TKO-500 and TKO-600 seem to be very popular. I will be going for the latter because of my HP. Both are 5 -speed.

You might get more technical responses than mine! I spent nearly a year asking lots of questions here and researching!