Quick follow-up...
I recently discovered that the original MFJ 422-X keyer (non-B or C suffix) were all sold with an original 16-pin Curtis 8044B chip. Later Curtis chips were either 18 or 20-pin devices as discussed above. This means the 16-pin Curtis chip can be extracted from the MFJ keyer and used in the Vibroplex EK-1 paddle for Mode B operation or in my case, used in a Curtis "Lil Bugger" keyer.
The MFJ 422 came with a Bencher BY-1 paddle while the "422-X" version could be purchased as a stand-alone keyer but can still attach to a Bencher paddle.
Used 422-X keyers can be found on the used market; a lot of them were sold in the mid 1980s. I recently found a few in butchered condition but the Curtis chips are fine.
Paul, W9AC