[chris vickery]

Just an FYI for those who are unaware,
the flathead motor came in 3 sequential versions;
1937-41, typical with the diver helmet distributor
1942-48, typical with the crab style distributor
1949-53, typical side block mounted distributor similar to modern style
I would think that very early carriers such as the MK1 might have the earliest block with the divers type. They were inherently known for electrical breakdown due to burning up coils due to the location deep down at the front of the motor and intense engine heat.
The 2nd version (crab) used the remotely mounted coil atop the engine to get away from this problem. You can adapt an early block to accept the 2nd model dizzy but it requires the timing cover plate from a 42-48 engine as the mounting is different.
Any flathead I have even done, I have made sure to go to the 2nd version.
Changing coils on a diver helmet type is a PITA.
Also the only way to properly time these distributors is to do them on an original timing fixture. I have had a couple arguements with guys who insist the reason their engine is running so poorly is because of this or that etc. Time and time again, it is the distributor.(bad coil)