So then the initial two consensus is indeed, the 7308s will perform as needed without any issues with voltage, etc. ...Thanx for the input fellas...
6DJ8, 6922, and 7308 tubes are all of the same family, and should be interchangeable (haven't heard of 6DJ9's before - Maybe a typo?)
I've personally swapped them around in my current preamp and previous phono preamp.
From what I remember the only really difference is that the 7308 was generally used for military purposes so they were held to higher tolerances and purer materials - There of course may be other differences as well, but the voltages should be near, if not identical.
I believe the 7DJ8 has a slightly different plate voltage, but some people have reported (also on this thread) that they work fine as a replacement.