Engine Serial numbers

I have searched this forum from top to bottom... and maybe I need to go to a M38 forum for the answer.  I have 3 CJ2A's and 1 M38.  I purchased all of them from one individual.  I am trying to figure out if I have all the original motors and which jeep they are in.  Two motors have serial numbers starting with J... which I understand are civilian motors.  I have another motor with a serial number starting with MC.  It also has a large R stamped in front of the MC.  Does this serial number starting with MC mean it should have come out of my M38?  Any info would be great.  Thanks!

the MC would be a correct engine for the M38, the R stamping probably denotes that the engine was rebuilt.

Thanks for the info.  Others have posted that the engine's number should be around +/- 10000 to the serial number.  Which is true for each motor I have a number on, including the M38 to the motor that starts with MC. 

Can someone point me in the right direction for a book, document, or thread that lists casting number breakdowns?  I am currently trying to gain info on several engines I have recently picked up.  The block that was in a CJ2A I am restoring is junk - a crack down the length of cyl 1. 

I have a 1946 CJ2A in England, although it was imported from USA about 7 years ago.  Its serial number is 78792.  The block casting number is 638632, which I understand makes it a very early block, and the engine number is J80365A.  This seems close enough to the vehicle number for it to probably be its original engine.  The cylinder head is a mystery though.  It doesn't have the Willys Jeep logo cast into it, it is not ribbed but it has a casting number 637014 which I haven't managed to find any reference to anywhere on the internet.  Can anybody give me a clue please? 

Mike, would the MA head have the two bolt thermostat housing instead of the more common three hole one?

Looking at Low's link answered my question, MA head has the two bolt thermostat housing.

Hello again.  Yes, this head has only 2 bolts holding the thermostat housing in place and has the original housing with it.  It has no cracks that I can see and on a compression test the engine pulled 100 psi evenly across all cylinders, so I think it's a good one.  How on earth it came to be on the CJ2A I've no idea.  It does have a heater take off let into it, but that looks like a proper job. 

Anybody ever see an L134 engine serial number that looked like this stamped on the S/N boss above the water pump? 4LR115547A I have yet to look to see if there is a S/N stamped behind the oil filter. BTW, this engine is in a '47 CJ-2A S/N 147748. Any info is appreciated, Geo:)