Don-
I see a few issues with what you are trying to do with your 450. One, if your loader is on a 129, that tractor would struggle to run a 450 normally; you'll waste even more power by running it from a hydraulic motor instead of through a belt. I don't think the 129 would be able to keep up. I think those two-stage blowers need 16-18+ hp to work well. 12 is not going to cut it. It's probably only going to get 7 or 8 at the blower with your idea.
Also, I think it'd make more sense to get a different (as in CHEAPER) blower from some off-brand tractor and use that instead, since you can mount the hydraulic motor in practically any orientation. But your biggest issue is going to be the one I mentioned above.
You've got tons of tractors, just put the 450 on the 1512 you have, or the 1811 you just picked up.