Clear & Accurate Points !
I think this would be more work than what the final result would achieve.
Depends on your final goal.....
Don't get me wrong, I'd like more power from the 750 as well. However, if one were to upgrade the heads and pistons, there would a lot of internal work that would need to be done. Hoaning the cylinder walls to allow for the larger piston head, may need different valve system, may need to update internals through out engine to handle extra power, and anything else I may have missed.
There is always a risk when upgrading internals. But you can't just focus on one area and hope the rest holds up. A guy/gal who spend what time and money they have to build the 750 with 1500 heads and piston just to watch the crank case explode seems futile to me. I know on crate motors, it is a common practice to use smaller heads on a larger engine to increase compression. I had a 355 setup like that. Had 305 heads on a 350 block. Gave me a 10.x
(can't member now) compression ratio.
I think the better option would be to find a bigger engine which could be adapted to the bike. The VN1500 is a drive shaft bike, so maybe the parts are adaptable. Would also need to modify the frame and engine mounts for the larger motor.
Def be cool if someone figured out a way to swap to a larger motor. Be like a fox body mustang from the 1990's have a 351 Cleveland or larger motor stuffed under the hood. Or better yet, a classic VW bug with a small block V8 stuffed in it.