On a 6" rim 185 would be about it, 195 would be better for fit. Drop to a 60 series and that should give you a lower height. Look at my old deuce on the last page of my gallery, that was a 195/60-15

Here's another tool that's tire related you may have use for, though not exactly what you're after on this thread.

http://www.mindspring.com/~cinque/test/tirecalc.html