I'm starting to work on the 1959 GE that I got from Dwight, the 21DEP4 CRT works but is tired, it was replaced in 1964.

I have a new 21DFP4 in another set that I'm less interested in so I'd like to swap them if that's possible.

Looking online they seem to be identical physically but I can't find the electrical data for the 21FP online anywhere.

The 21DEP has a list of tubes it replaces on the label but the 21FP isn't one of them. :headscrat

Disregard this, I seem to have the answer now, looks like it's a go.