I read that 4.o Mj's are MX but mine is 712m16.
It is a pureblood renix that only saw a tow truck when I lost the clutch slave 50 miles from home. The slave was changed at 305,000 and the clutch itself was still a good clutch.
I bought this truck new in Feb of 88 and ran it to 320,000 when I heard a slight rod knock. Not a tappet but a rod. Sat for 4 years, put a battery in her and she fired up on the second start up attempt. Rod noise was louder so she is in the garage getting stripped down for a trip to the machine shop.
I was amazed that there was no ridge at all on the cylinder wall.
Anyone know the deal with an M and not an MX on the build code?