Need some help with tire choice

[GMC91]

I dont know if this is the correct place to put this but since tires deal with suspension, Ill put it here. I got a 76 C-10 that I am currently building, and Im getting close to paint. And the next thing after paint before I can drive it, is tires and wheels. I am gonna run 8 in rallies up front and 10 in rallies in the back. Future plans are for a 4/6 drop on the truck so that will have to be factored in as well. I am not running inner fenders right now and plan to build some custom ones later on. So, I need some help deciding on tire size and I need to find them for as cheap as possible. I will have around $300 to spend right now. So I might have to buy 2 new ones, and transfer the ones on the front of my truck now to the back and put the news up front till I can get new for the back. If anyone can help me out, it will be much appreciated.