OOPs - Forgot to add that I have been told that the 292 block is about 7/8" longer and the waterpump is longer as well. I have seen a 292 in a large (1 1/2 ton?) '51 chevy. The radiator was moved forward to the other side of the mount and moved forward. Apparently there is more room behind the grill in the older trucks. Possibly if a car bellhousing was used, along with a passenger type rear mount the engine could be moved back an inch or two. As soon as I get my truck to a place where I can work on it I will give it a try. From what measurements I can make now it looks like about 3" more room is needed.
