Early block drain tap source?

[Mike_S (Mike Spoelker)]

Prior discussion:

Coolant drain tap XK120/140

Me again! Is the thread different between the engine and radiator drain taps? They look similar but the radiator tap is C980 and the cylinder block one is C2354. I have what I think is an XK140 rad drain tap with a soldered-on piece of downward curved copper tube. I like the design - would it fit the XK120?