Weight. They are heavy compared to the LA engines. Valve layout is like the BBC, 385 Fords and Cleveland Fords, but preceeded all those.
They were a lower cost to produce than the hemis. The LA series is lighter and was lower cost to produce.
Wait again. Put aluminum heads on it then it will weigh less than a LA. And while you're at it keep in mind the head design produces more torque than the LA head.
