Ok so I'm a bit lost on some info I've seen. Are there are other 13b's besides the 13b in the Rx7 that are N/A? Well here's what I'm looking for:

I want it to stay N/A. Whether its a taking a stock 13b as far as it will go legally ( or semi-legal atleast) or finding some long lost Cosmo engine and starting there but what N/A (if others exist) would be the best starting place? I said 13b earlier because I don't want the hassle of the 20b. Any advice would be appreciated greatly.