Silver Bullet - I temp mounted my 600 & ran a chain down to the impeller shaft, then on-trailer-tested at ramp. I thought you might want to hear about my findings.
The 600cc (YZF600R) engine pulled fine, didn't have a tach but estimated by ear 7000 RPM (the pump's designed RPM). It was in high gear & had some throttle left. Your 1000cc should pull even better. It started in-gear no problem (I didn't have the clutch hooked up).
2 things are clear:
1) The exhaust pipe (was high & dry) was mega-radiating heat. Fabbing a wet-exhaust is definitely the next key step. If I can't make something safe for under deck, then the whole concept is dead.
2) I found the jet pump's cooling water didn't start flowing until about 2K RPM. Part of that might be that the engine was mounted above deck (up high temporarily). But I think your design of wet/wet cooler is the way to go so that the engine never runs empty of coolant. So I may be copying your design
.
Good luck on your build!