My Dad is looking for wheels for his 1979 GMC 2wd 1/2 ton. He is doing a 3" spindle drop in the front, and a 4" drop shackle and hanger kit in the back. We have been looking for wheels and we're not sure what backspace and offset we will need. He wants to run 17's in the front and 20's in the back. Any help you can give me would be appreciated. Thanks in advance. :)

Check out http://67-72chevytrucks.com/

There is a group over there that is well versed in mods, etc., on vintage Chevrolet trucks.