That number is the Serial number, not the casting number. The casting number will be found towards the front of the engine on the RH side near the bottom of the block.
Unfortunatly, the codes I have only cover up to 1 ton, so I can't really decode it too far for you. I can tell you that the L in the code does equate to 1953. I do know there is a site with the codes, but I do not know the site name.
