Just been having a bo-peep at some of your images, what caught my attention was the image of the LHS of the engine block with the stencilled number 537.
That would certainly indicate to me that your early 2 1/4 lt engine was out of a S2 Command/Recon or S2 109ex mil, but it would be a time consuming task to look up the engine numbers to find out 100%, anyway keep at it, it is looking good, cheers Dennis.

