not too sure about pulling with spacers but I do know the trucks in the tractor pulls, some of them are using the wheels spacers, if those spacers can handle 400 hp and above then you should be OK, but don't take my word for it, I could be wrong.

just make sure you get really good studs.

 

you have a Dana 70 rear, not a 60......

 

I dint think the problems with teh spacers would be teh HP. That more in the studs. I think the issuse would be load (weight) on teh axle.