Hot Rods Flathead cam face contact differences for Distributors

I am going to post this for future reference.
I ran into an distributor issue changing 59A engines into my pickup.
After reinstalling a front mounted MSD ignition into a newly rebuilt engine, I couldn't get it to fire.

After many days of trial and error I realized there was a difference in the distance between the mounting surface of the distributor and the cam face. Here the distributor snout wasn't even reaching the cam face to engage the distributor.

Measurements found the newly rebuilt engine had a cam face .500" deeper than the old engine.
Has anyone found this problem during rebuilds with aftermarket cams?

 

You probably need the quarter sized .500 thick offset drive "thingy".

 

Cams used 1932-1941 had a protruding nose very roughly 3/8" or so longer than 1942-48. Visually, the early one protrudes significantly out from the face of the cam gear while the late one is about flush.
The '42 cam became the service replacement for all and almost all aftermarket cams are based on the late cam, usually noted by its Ford prefix 21A in cam catalogs.
Ford supplied a short button that extends the late cam to replace early, and it is still sold by all the Ford suppliers...not expensive either.
The button and spacer plate adaptors of a couple kinds allow assembly of any combination of '32-48 distributors and cams.

 

cam adapter
Late distributor to early cover

late distributor spacer for use with long cam

 

Thank you Bruce. You know, now that you brought that up. I do remember reading about this.
Boy am I glad you have a mind like a steel trap. Thanks for adding your info for future generations.
On the MSD distributors the (cam) contact end is removable and made of steel. I plan to either remake the snout or extend it to reach the cam face.
Rick