Back to basics
Welcome to FABO. You've come to the right place 'cause there's no shortage of opinions here. As Moper said, you've seen a lot of different combinations from a lot of builders.
I've got to applaud your research as I'm trying to do the same thing in my '69 Dart build - lots of research and only a one-time purchase of the right parts in the right combination.
Luckily, my choices on some of the major parts was made when I originally bought my Dart. It came with a brand-new 380-horse 360 crate motor, 727, and b-body 8.75 rearend. All good starting pieces IMO.
Again, as Moper already said, let us know the specifics on your car, your intended usage and where you want to end up, and an approximate budget.
We'll be glad to spend your money for you!