What is the backspacing or offset on stock wheels?

[rennat_2006]

Hi first post here

Ive got a 77 chevy k10 and im lifting it 4 inches and going to run 35" mud terrains of some sort. It is my Sh*tbox that i picked up for $500 just to take out and beat on instead of my 2000 Zr2 blazer that has had double duty as the weekend wheeler and weekday daily driver. I had to get something cuz ive already sunk the blazer in the river up to the windows...But thats another story.

Anyways im trying to figure out what the factory wheel specs are concerning wheel width and backspacing/offset. Im going to buy some new wheels and need to know what the factory specs are so i can order the right backspacing/offset to get the wheels out of the fenders an inch or two.

Any recomendations for backspacing/offset for a 15x8 wheel to get the wheels/tires out of the fenders like im wanting?

Thanks