390 vs 408

If you put real pistons in it (meaning forged, not the hypers) then the cost for the 390 is a little more as not everyone has a piston for it. Otherwise, same same. If you have the 318, use it. It's prob cheaper than finding something near you bigger. There will be more bore shrouding, and I agree it's around 6-8% loss in all lift ranges as a result. Only you can decide if that's acceptable. I had plans to build one for my plow truck but that changed. I think it's a great potential engine. But eventually when looking for max power the bore size will limit things.