Wheel backspacing/offsets

[Leadfoot]

Anyone know the right backspacing/offset to put the widest wheel in the wheelwells for my '68 swb? I know a 10" wheel will fit out back, just dont know the correct way to measure. I want to put 20x10's out back with the biggest lip possible, just dont want them sticking out the wheelwells. Just picked the truck from a guy who got it out of Vegas so its a perfect project. It will be lowered 5" up front and 6" out back.

[ChevLoRay]

I put a pair of 15x8's on the front, and 15x10's on the back of my truck. The backspacing on the front is 4-inches and on the back it's 4.5-inches. I realize the overall diameter is different than your choices, but the backspace should be similar. ECE was a good resource for me, when it came to proper backspacing. You can email them, with your question, and they will steer you in the right direction. My thinking for your front end is that wheel diameter plus drop will mean you need to can the inner fenders.