The mid 70's blocks should be no problem for building a moderate horsepower motor, just not a race engine, from what I've read. The bigger issue might be the motor mount holes. They changed the motor mounts from two bolt to three bolt in 1970. The early 70's blocks have all five holes and some of the mid 70's blocks do to. But there are some mid 70's blocks with only the three holes so you need an adaptor to bolt it up to an FGF.
