Why would you want to use a cable tranny? Im not positive but I think you'd be replacing differentials alot if you match that up to a b18. Those trannys had pretty weak differentials as well as synchros.
As for the thread jacker - yes an s20 tranny will work fine but I'd advise you go for an ex/si one (b000). I have an s20 b000 and I actually like it better than the s40 that I had before...