can you lay frame with a 15 inch wide rim

[topher]

I am building a 69 c10 full air ride with a step notched rear frame and i am away working at the moments and a friend found me a set of 20s the fronts at 20x8.5 with 4.5bs witch will work perfect but the rears at 20x15 with 6bs. if i was home i would go measure it myself but i am not can someone plz tell me if there is enough room between my box sides and frame rail to tuck a rim the large.

http://www.truckinweb.com/features/0...c10/index.html

i found this truck so i am thinking it might work