1960s Sylvania Color TV Console Issues

[Electronic M]

Unfortunately that sub is probably not going to work. Around 1968 a law was passed that changed tube size measurement from outside bulb diagonal to viewable phosphor area diagonal (which is around 2" smaller) and newer tubes that use viewable phosphor area have a V as the first letter and usually 4 letters. So a ~1966 tube like your 25AJP would become a 1969 23VAJP.
The 25VDMP you're looking at is going to be 2" bigger than the 25AJP so it's probably not going to fit.