Ok I have the dimensions for the '89 ext cab short bed and the '87 regular cab long bed. Looking at the side of the truck. Cab mounts are the same on both trucks it is 43 1/2" center of bolt to center of bolt. The wheelbase for both is 116" pennyman1 was right on that one lol. The bed thing is another creature but it's workable I believe lol. anyways on the ext cab bed front mounts are 8 1/2" they sit real close together. The reg cab is 19 1/4" front bed mounts are spaced out pretty good, but the kicker is I measured from the back cab mount to the 2nd cab mount is 27 1/2" on both trucks so I was thinking on cutting the front bed mounts on the standard cab and keep the 2nd bed mounts on and attach the short bed to that. The rear bed mounts on the long bed are 13 1/2" spaced out a good bit but the short bed mounts 8" kinda close together but I can drill a hole in the bed and bolt down the short bed on the rear mounts like the old trucks with a carriage bolts. If the mounts don't quite line up on the front mounts for the bed I can do that to with carriage bolts also. The cab at least line up good enough just have to cut the front bed mounts cause of the ext cab being long.