From the OP, it's impossible to tell if you know what you're doing at all or are just stating stuff that is commonly, though not necessarily accurately, said about old tube amps. So it's hard to make suggestions, other than (1) follow all safety practices, fully; (2) do all basic inspection, servicing, troubleshooting, and testing before you jump into categorically stripping out original components that may be fine and better than anything you can replace them with, and (3) power up slowly with a variac to the correct voltage for the amp/year. BTW, "untested" commonly means "broken." It's how people commonly post stuff, covering their butts, in a manner that doesn't leave them open for returns and bad feedback when they ship something that's DOA. Obviously, most people are going to test something that will yield lots and lots more money if it works than if sold "untested." Much "untested" stuff is actually non-functioning, "ignorance is bliss" stuff. Of course, even dead equipment can be a good purchase depending on what's needed to repair it (and if it's not modded/messed up by the owner). Good luck with what, when working, is a good amp.