I got off the phone talking to Clausing. The findings are as follows:

1) Outside spindle taper is LO (which I knew)
2) Inside spindle taper is "MT3 with bushing", the OD of bushing is of
unknown taper and Clausing does not know anything about the OD of
bushing.

So, I think that I will return the MT5 test bar that Steve L so
generously lent me, and will try to find some other way of testing
this lathe.

i