How big a mountainbike for 80cc motor?

[TonyGotSkilz]

Hello all, i'm looking around for a good used mountainbike to complete my $200-250 motor install (bike (X) + motor ($160) + install ($25) for that price) and i've found a few candidates but nothing solid yet. My main question is how big does the frame have to be to accomdate the motor? I've noticed that certain types of bike just look like they won't work (mongoose for instance) and i found a nice cheap bike that looked great but it had a 17 inch frame and i'm 5'11 btw. So i don't think that would work for me or for the engine fit? What do you guys recommend for a guy my size. I weight 170lb if that matter although i doubt it.