Don-
I'm glad Steve B chimed in on this one. My "seat of the pants" brain was thinking what he said, but I didn't know if it was correct. Being an engineer by trade, Steve knows how weight distribution works.
Having said that, Robin's set up looks to be a really well designed and built set up. The #450 blower lift set up sucks, so I think you're smart to build another option if you want to make it better. I always wanted to make it lift hydraulically with a small cylinder out front, but never could figure out how to mount it. Now that I understand how the current lift system works, it's been fine for me.
I'll add in some thoughts on rear weight. My 2072 has #100 on each rear wheel.
This was "barely" enough weight to get good traction, (I'm #240) but then again, this is with the wider 26"X12" tires, so I would think that #100 on your narrower 10.50s would be fine. If you're going to be adding a Sims hard-cab, then you'll have PLENTY of weight. I noticed a HUGE difference in traction after going from the soft-cab to the hard-cab it has now. These steel and glass cabs are heavy.
I always think of weight as a balancing act. Too much weight on the back is going to eventually take away from steering. If I'm blowing snow and accidentally "hook" the edge of an existing snow bank while clearing the driveway, sometimes the front wheels will lose directional control. (tractor continues straight although the wheels are turned) Lifting the blower just a tiny bit (1/2") adds weight to the front end and helps gain front traction again. Once the tractor pulls away from the snow bank, the blower is lowered and all is well. It's kind of like dancing, only this woman weights #1,000+, smokes, and is loud.
LOL
Since your tractor is a diesel (heavier engine) it may respond differently with regards to weight distribution. If I were you, I would just hook up the blower as it is, add #100 of weight to the back and use it like that. Once you get some use out of it, you'll know what it needs and what it doesn't need. Right now you're kind of trying to fix a problem that may not be an issue worth worrying about.
Hope my rambling helps....