like
@318willrun i just buy for what i'm building and match it to that.
i do know that you want around 1 ohm and too much one way or the other risks overheating the coil or smoking the box.
if you're starting from scratch you might be better of buying a kit, or part of a swap kit to get the matchy-matchy part of it out of the way and then figure out a distributor.
i'm sorry, i know that's not of much help.