I,ve found them in mid-'70's Broncos as well. Got one laying in my backyard now. Visually, the only difference I've seen is that the main caps are beefier; instead of a 'ridge' going across the cap from bolt-to-bolt, the caps are full thickness, thus stronger. On the outside, there is a 'nub' sticking out from the front of the block on each side, on the left side in the area of where the fuel pump sits. Have heard both ways as to whether they have better alloy in the blocks or not. I'd imagine a machinist who has worked on one could tell you if they are harder than a US block.