First off you need to check what standard the 1-1/2" X 6 tpi. the spindle nose thread is.
1. Is it Whitworth (55 deg)
2 . Or Unified (60 deg.)
Dependant on quality of manufacture (closeness of fit) of accessories sometimes mixed standards will work one way but not the other.
I have a later electronic drive version which is 60 deg. and had an older mechanical drive version for a while which was 55 deg., they were built to different overall dimension standards as well, not just the thread and chuck/faceplate register diameter and depth.
I would not be surprised if the spindle nose thread specification changed during the life of the mechanical drive 28-30 / 40 or 38-40 machines production.
Most of the readily available 1-1/2" X 6 tpi. fittings are 60 deg unified.