youll need a head(i like noss), domes for 4mil, 4mil crank(i like hot rods), good clutch, depending on the syle of port work you might need bigger carbs, intakes,pods.. as far as the trans goes it depends on what your using the bike for..if its a drag bike then youll want an override, if its a play bike, stock trans should be fine as long as its in good working order! complete gasket and seal set! depending on what pipes you have now you might need to upgrade for full potental! im sure im missing some stuff.. your best bet is to call a reputable builder and go into great deal on what you will be doing with the bike and they will take it from there!! i had fast racing do a 4mil stock cylinder that i liked, now im currently running a 421 cub that redline did witch i love!! i have had GREAT dealings with both! a buddy of mine is running a 4mil stock cyl. that was done by herrs and that thing hauls the mail as well!! good luck