The gearbox and everything forward of it is absolutely identical, bolt pattern, bracket interface, etc. It's only the depth of the motor that's different (and only the depth - not it's area). Without having RV-7 plans in front of me, I can't comment on the clearances. But you'd need to be able to accommodate an additional .93" of motor length.
We can't say we've heard the same thing, save for one customer that we sent bigger servos as an experiment. We've had reports of some slippage in turbulence, but this is neither unexpected or unacceptable.
Also remember that the SV42 is heavier and will add a bit more drag on the control system (stick feel).
But, if you want to (or know someone) that wants to give it a go, by all means.... We'd recommend that you try the SV32s first, though.
