A GMC 302 crank is a 302 crank regardless if it came out of a military or civilian. I have some of both. The military vibration damper used a 7/8 pulley which means you need a 7/8 water pump pulley and generator pulley and they are difficult to change because the clearance between the fan and the radiator. GMC used a 3/8 belt in their pickups from 54 on up and they fit on a military crank. The 1 1/2 inch difference is the difference between Chev and GMC. GMC 228, 236, 248, 270 and 302 are all the identical length and these engines will bolt into a GMC from 1939 through 1959 up through 450 series.
I have known Patrick for over 30 years and I still have a NOS 302 that I bought from him at a time when he needed money. He has always had the idea that GMC vibration dampers slip. After they get to be 60 to 70 years old, they probably do, but they can be rebuilt to last another 50 years.
Where the idea came from that a 270 crank weighs 5 to 10 lbs less than a 302 crank is beyond me. If you look in a GMC master parts book, a 2404929 crank fits both 270 and 302. The military block is different in that it doesn't have a hole for a fuel pump, but the lobe is on the crank. It is possible to cut a hole in the block for the fuel pump. Also there is a locator block on the military block that was unique to the transmission setup used in the military trucks. The block must be ground off to mount a civilian starter.
I think the drilling and tapping myth got started with the older 228, 236, 248 engines that had a press on vibration damper. They also have a 4 bolt flange for the flywheel. Later 248, 270 and 302 have a 6 bolt flywheel flange. It is a simple matter to drill and cut threads in the old cranks to accommodate a bolt for safety.
