What is the difference between a ford 351 Cleveland square block and D block?

Answer 1

The terms 'D' block and 'square' block apply to differences in the casting of the Ford Cleveland engine block. This difference is visible on the block just in front of where the left head mounts where the fuel line usually crosses over. This casting mark either looks square or it'll be in the rough shape of a "D". The 'D' block is the earlier casting, in fact the initial casting of the 351C block and the 'square' block is the later one. How much later is open to conjecture. 'Square' blocks would appear to have been available in the U.S. in 1971, and there is some evidence to show that the 'square' block appeared in automatic XY 351C 2V's as early as May, 1971, and in manual XY 351C 2V's in December, 1971. It does appear that XY 351C 4V engines continued with 'D' blocks. What can be said though is that no XW or XY GT came with a square block, and that all Australian built engines are patterned after the 'square' blocks. All the 1971 Boss 351 engines were all square blocks. I know that the 1970 351C 4-V M-code was a "D" block.