I am by no means a pro so if I am wrong please correct me.
There isn't as much choices with rims for 8 lug compared to a five lug trucks but there are some available. I think there is some at summit if you didn't check that. Are you looking for less then a 16 or more? Go here
http://www.discountedwheelwarehouse.com then click 8 lug on the left.
I haven't bought any thing from them but they have many 8 lug rims in all sizes.
As for the lowering goes I think you could use blocks in the rear (if you only want 2-3in) as for the front you can cut one coil off for a 2in drop. That should be the cheapest way to go if you only want a small drop. Or you can go with Drop spindles in the front (got mine at GMCPauls)and they keep it 3/4 ton and converts to disc brakes if you don't have them.
Hope this helps.
100th post
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1970 GMC C-25 LWB (middle of frame up)
5-7 drop with 3in drop spindles, flip kit with blocks and still keeping the 3/4 ton. Shaved drip rails and marker lights, rear roll pan, cowl induction hood.
1987 Camaro z28
350, vortec 305 heads. 10:1 comp, t5 trans. Street terrrorizer.
1988 Monte Carlo (Super Stock ashpalt race car)
My Truck