There's nothing actually wrong with using a rear induction engine for CL stunt so long as the port timings are suitable which would generally make most RI engines unsuitable because they're usually set up for high power at high revs. That said, MVVS had a rear induction stunt engine (a 56 IIRC) which one of our better flyers here in Australia swears by. The only real disadvantage I can see is that they'd be more difficult to prime unless there was an opening in the side of the cowl to get at the intake. A slight advantage is that it would put the intake much closer to the tank.

The 40 VF's gathered a wide following in CL stunt for two reasons. The first was that they gave a lot more power when piped (about the same power as a muffled ST 60) which allowed the the use of thinner, less draggy, lines because of a loophole in the AMA rules which based line diameter on engine size, the cut off being over a 40 size engine. The second reason was that the VF's have very mild timing (actually identical to some well known CL specific engines) so they didn't need to be revved hard and could turn large props for high thrust. Interestingly, although VF's have been used for many years now, I haven't heard of a single case of liner peeling but I'd put that down to the fact that most CL flyers use a generous amount of oil in the fuel and the lowish (~10,000) revs they're run at.