Just a couple addendum's I think the 421a was absent since it was discontinued years before the list.

If the 421 is original would suggest using the 8H specs, Same cone but higher temp coil.

If reconed, current parts are closer to the 8hII.

Suggestion? Post to CL to see if there is a neighborhood geek who may be able to measure yours. Some guys would do it just for the fun of it.