What you've drawn will technically work, but I have a few small complaints:
1) You're wasting a four pole switch (per channel) when a two pole will do. Essentially, the upper and lower poles are just acting as terminal strips. In one throw, they connect the plate to the transformer. In the other throw, they do the same thing. They aren't actually switching anything.
2) As you've drawn it, you want to be absolutely certain no one is ever going to inadvertently throw the switch while the amp is running. There's more than a few henries inductance in the output transformer's primary winding, and you've got over 500 volts potential to start. Opening that switch is going to cut the tube current from 70 mA to zero instantly. I'd expect to see at least a couple kV across the switch contacts for that instant. Not good, and a recipe for a short-lived switch (at best). Of course, it probably isn't good to be switching the UL tap hot either.
I think there was something else, but I've lost it now... Anyway, if you've already got the switches and really want to use them, maybe consider rearrange the plate leads a little bit. Otherwise, just use a two pole switch and mount a small terminal block nearby, land the plate lead to that, and use it for attaching the resistor.