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There are several web sites concerning the M151/A1/A2 "Jeep", it is technically a truck, not a jeep. The Military Vehicle Preservation Association will have some good leads for you. If you do not have any experience with these types of vehicles, I strongly suggest that you spend lots of time researching the M151, especially the peculiar handling characterists of this vechicle. My first four years in the Marine Corps I spent driving these, belive me, if you don't pay attention to how the M151 handles, it will roll over, regardless of what anybody with no experience with an M151 may say.
The engine in that thing is a Continental engine, you won't find it much of anywhere else as it was built and used only in M-151 through the A2s until the cessation of production. It is about 140CI as I remember look around on the web there are people who sell the parts for them, be sure and keep the universals lubed, all twelve of them and they will hold up better with synthetic grease for that matter use synthetic gear oil in the differentials and the tranny also as they are a bitch to get also. I've seen tops and other stuff advertised for M-151s and I've seen them sold restored for 11 to 14K, good luck. (If you like real 4x4s check out the Pinzgauers)
Look for a Jeep service manual on ebay - it should have the info you are looking for. My father has a service manual for a 1967 Jeep but he is unwilling to part with it. I can make a copy of the engine section and mail it to you if you want. Just email me at rdavis21@pacbell.net