Early Knucklehead Lifter Block Identification

[shinedogg]

Hey Fellas,
What is the easiest way to identify early blocks from later ones?

[MMasa]

The chamfer at the top where the pushrods tubes seat.
Early blocks have a plain counter bore with a square edge.
Later blocks have a 45 degree chamfer at the top of the counter bore.
Mark

[shinedogg]

Thanks Mark