what should be out there as a "kit" is and correct me if I'm wrong because this stuff may be available ...a 340 style positive deck domed piston kit for a 318 block, or a flat top zero deck with fly cuts pistons etc I would do that with a 318 with the aftermarket heads...but the 318 is limited with what can be done it can only be bored so much etc. I don't really think 3.91 is a big issue its just what parts are available for piston kits, sroker kits etc. and of course cost effectiveness what you pay for how much power in return. I know I tend to overthink these things...