depending what kind of budget you've got the falcon can be done to a big block.... but its easiest and cheaper to stick with a smallblock.... and even then the 351 is a tight fit..... but you could fit a well built 302/347 in there easily..... and relatively cheap,,,, you just gotta weld up the shock towers, change your motor mount brackets, sway bar, add a shock tower bar, get front spindles for 5 lug with discs and get an 8 inch or a 9inch rearend.... you will also want to get the tranny rebuilt.... i did the same conversion on mustang and the tranny for the 6cyl just couldn't stand up to my 302 for too long, blew in a matter of weeks...