I have a 52 F-1 with the flathead. Lots of mods to it and also a 4 speed T-10 behind it. Why not keep the flattie? If not, hell, use the Poncho and be somewhat different. Just my opinion. Next choice would be the 390 (keep a Ford in a Ford, ya' know!). Lastly, could be just like everyone else and put the Chebby in. But why?