RE: GP290 vs. G260
Thanks for the explanation SavageJim. That wasn't quite what I was asking, but I was still curious about that as well, so it was still very relevant. I was looking around a bit on DDM's site and I kind of figured it out for myself. It looks like ESP does the mods like you were talking about in your post, while DDM does the race porting where they enlarge/reshape the intake, exhaust, and transfer ports. I'm guessing these are two different processes.
So this begs the question, which is more beneficial? ESP modifiied, or DDM Race Ported? On the top end kits, it looks like the "claimed" horsepower on the DDM Race Ported top ends is usually the same or more than the ESP modified ones, but I get the feeling that they may be a bit biased about that.
FYI, these questions are coming from me mulling over splcrazy's idea of a zenoah crankcase with a modified top end kit.