Is there any risk of running an offset of 4.50" in front and about 3.75" in the rear to balance it out?

Wheels are ProComp streetlocks.
Tires are 31" STT's which are currently on stock GMC alloys with no rubbing.

 

There shouldn't be any problems with this. It's no different than a lot of people who add spacers to the back, or change out the rear axle to even things up with the front. The only issue I can see is you'll have to do be careful when rotating your tires. The front tires wouldn't be able to be rotated to the rear without changing the tires on the rims.