Were all Universal carriers 6V?

[chris vickery]

The diver's helmet style distributor is typical for the UC.
One of the main reasons of ignition failure on the flathead engine is due to overheating of the coil, which UCs were particularly prone to. The distributor being placed so low on the engine and tucked down in behind the rad lent plenty of opportunity for coil failure.
Old coils are especially bad, throw the original away and buy a reproduction.
Many guys opt for a remote coil with an adaptor plate which fits the diver's helmet style distributor.
Optionally, you can use the crab style distributor which already comes equipped with a remote mount coil. You must change the timing cover plate to accept the crab type as the mounting is different from the diver's type.
The diver helmet was used on the 37-41 flathead motor, the crab went 42-48 and the common modern type was used on the 49-53 model.
The upgrade to the crab was a result of the diver helmet type being problematic, hence Ford's solution with the crab style.
The UC restored to spec uses only the diver helmet type as far as I know. I do not think that they were ever updated to use the crab type unless someone else knows better...