If you were going to rebuild a diamante motor, I suppose you could always put the Montero pistons instead of the Diamante ones. I'm guessing that's what is changing the CR ratio, but it still may be an interference motor due to the change in valve timing. That's just a guess, Frank and Old Colt seem to know a lot more about the V6 though.

When I worked in the machine shop, we used a general rule of 4hp per compression point change (if nothing else was changed). That was a rough number we've seen on dyno pulls. Some gained more but most were in that 4 HP range. We had a few customers that thought raising the CR was the secret sauce no one knew about, despite us rebuilders telling them to do just some basic valve bowl blending, a good 5 angle valve job and just smoothing out any obvious casting flaws in the air path would net a larger gain (we usually saw about 15-20 HP on a standard V8 with just some very minor head and deck work to even things out - kind of like a poor mans blue print job).