Why do i need adjustable pushrods?

Well, so much for that theory. In Larry Shepards book 'How To Hot Rod Small Block Mopar Engines' he states this: 'Pushrod overall length is another important feature. All the A-engine hydraulics are the same length up to 1985.
Engines after '85, as well as the newer 318 roller, are the exceptions.'

Is it possible the heads you used are from after '85?

Just another theory. Mike