Engine swap

I have a '69 Fairlane that currently has a 250 cid six. I have access to a 429 "Thunderjet" w/C-6 transmission, or a 351 Cleveland, no trans. Which would be the best choice? What parts would have to be acquired? The car currently has a 2.79:1 8 inch rear end. Would there have to another length drive shaft made for the conversion to the 429? Any help or tips would be appreciated.

that a 250 crossflow?
similar to what falcons run here in aus?
ive seen one of them run 500 odd horsepower.
sorry if i aint helping.