[MAR-Ktech]

Larry:
Your numbers are essentially correct. For your reference points use the bed to frame bolt locations that are on each side of the axle kickup since they are the same for long and short bed. You have shifted those 12" forward on the truck by shortening the frame 12" to correctly match the shortbed wheel base. On each frame rail the front bed to frame hole is 11 3/8 forward and 3" inboard from the hole at the front of the axle kickup. There is probably already a riser from the frame at that spot and it may or may not have a hole in it already for the bed to frame bolt. The '66 long bed did not have a frame bolt at that spot although there was a cross sill there. Measure back 13-3/8" from the frame bolt location just behind the frame kickup on the rear of your frame to locate the rear sill mounting hole location. The rear sill is the same for short bed and long bed so you can figure the wood board positions front to back using the rear sill as your reference. I think your concern may be due to the front cross sill and mounting bolt is 3 inches back from the front of the wood on a long bed (matching your bedside holes) and is 3-1/2 inches back on a short bed. Make a new square hole in the bedside flange at the 3-1/2" location so the cross sill will be in the stock short bed location. The more things you can keep as stock dimensions the better, especially when replacing parts like bed strips and cross sills down the road. Consider purchasing a set of short bedstrips with holes that you can use for a pattern of exactly where the cross sills and reinforcing strips go.

Interesting project, keep us informed.

Mar-Ktech