I have converted several Pro295 and 2750. The cylinders are identical, as far as I can tell, other than the chrome plating vs. Nickelsil. The carbs are different, but mostly in the level configuration, I think.

Powerwise, they aren't different enough to call it one way or another. I do have come across a couple of refurbished ones that pull less RPMs than my other ones.

AV8TOR, I think the Poulan 42 will be a good engine for sport flying the WH 28% Extra. I stopped paying attention to the 3D fanatics long time ago. If you post in the Sport Flying forum, you might get some more realistic opinion. HOWEVER, I will have to say that the Poulan 46 would be a better bet. If you go electronic ign, the Poulan 46 is much better package IMHO. A bit more oomph, mounting is easier and the carb orientation (with the CH insulator) is exactly parallel to the thrust line.

The 46 is my all-time favorite conversion motor. I still do 42 for friends of mine that have the chainsaw already, but I always explain the caveats to them before hand so they know what to expect. Good luck.