For my money, if I buy a Fox 35, then a stuffer backplate, hemi head, ABC P&L, and Randy's crankshaft, I might as well buy 3 OSs, 2 Stuka Stunt specials, or a PA lite!
Well, if you order all from Fox it will cost $31 for the hemi kit and $65 for the sleeve and liner, but you may find a hobby shop that will discount that. Your first option will not perform as well, and cost more, but at least you can do that twin project. Your last option may perform as well but still cost more.