I'm wanting to build a SBC for max low-end torque for trailer towing. (Grew up driving John Deere's and a 292).

So how would it work to put a 400 crank in a 305 or 307? Would one work better than other?

Since I'm only looking for low rpm would the heads be a limiting factor?

The other option is a 366 TD BB

Thanks for any help.