Odd No4 number?

[jmoore]

This leads me to conclude that the serial number observed is the correct serial number assigned at the time of original manufacture. Thoughts anyone?

Given the plethora of "A" suffixed Fazackerlys observed from this time frame, my speculation remains that they were employing some non-standard mfg. techniques to expedite construction, so the "A" was a CYA. Most commonly observed to date are welded charger bridges. No proof, mind you!

The rear sight spacer noted above by Peter Laidler could very well be another.