Does that wet clutch one just bolt right in? I wasnt aware that they were interchangeable. I had that motor (nonvariated wet clutch guy) in a flandria apollo. It was very very slow, like 25 max and took a good mile to get there, but had a neat automatic engine disengage that would allow the bike to coast faster than the engine was turning.
I tried a lot of silly things to get it faster with basically no success. Your motor has the later piston port at least vs the wierd crank-arm inducted setup on the old one. I had one of each, neither was more impressive performance wise but the version you have is at least much easier