[COBRA406]

Was the number you gave located on the timing cover or on the passenger rear
side of the block under the head? Never seen a casting number on the
blocks like this one. As you probably know Clevelands were only made for
4 years from 69-73. 351M/400 production started with the 400 in 71. The
351M from 75 on. Basically same heads (2V) on all of them. 4V heads unique
to Clevelands. M blocks have 429/460 bellhousing pattern, Clevelands pattern
same as W motors. M blocks taller and wider than the Cleveland but share most components except intakes, crank, rods and pistons. I'll dig into my
manuals if you need to know exactly.