Measure the rear cross sill mounting spacing. If it is 39-5/8" wide, then the bed is a 60-62. If it is, then you will need to buy new cross sills and rear cross sill to fit a 63-66 frame. The 63-66 spacing is 7-15/16" narrower (or 31-3/4" at the rear cross sill).
And, by the way, I noticed you are in Norman, OK. We make the parts you need right here in Oklahoma City! See our website
www.mar-k.com
