If you want a V8 EB, then buy a factory V8 EB. Or buy a wreaked V8 EB and transfer the parts to your car. That would be the Windsor Motor, which is a 302. You can't convert a 302 windsor to a 351. You could buy a 351 Windsor from the USA, and get that engineered to fit.
The Cleveland Motor (302 and 351) is the motor where you change the rods and crank to convert a 302 to a 351. Clevelands are wider than the windsor, and heavier as well.
If you are just chasing the 300hp mark on gas, go for a 302 Windsor, and get that modified. You will have less hassles than if you tried for a 351 (either windsor or cleveland). Power to weight ratio is better too...
I've only heard of people importing an older style 4sp auto for running behind the cleveland. From what I've heard, it is a pretty good conversion.
Hope this helps.
'67 Mustang V8 4sp... what fun to drive!