It would be helpful if you had a schematic to post. I can't tell from the description if you're trying to build this to "switch" things while you're playing .... OR set it up so that you can change out tubes.
You can switch between tones somewhat by using a dpdt center off on the V1 cathode & paralleling caps and resistors. For example you can have 100k (plate) & 2.7k (cathode) with a .68uf in center off. Parallel a 10uf on one side and a 2.7k & 22uf on the other side and you have 3 different tones.
I think there may be a easier way of getting your son the different tones he is wanting? If you're just wanting a clean tone or overdriven tone .... there may be simpler ways of doing that. I personally would not consider using two OT's and switching between EL34's & 5881's. I'd just wire up the socket so I can change the tubes out and re-bias if you need both those sounds.
The other glitch you're gonna have trying to do this is notice the difference in values of the coupling caps and tone stack values between the Bassman and '87. Those account for a huge difference in tone. You could just build an '87 and then use the fat/full/bright switch I suggested & 5881's. Then if you wanted even a cleaner sound change the V1 to a 12AY7 and the phase invertor to a 12AT7.
This amp for example had enough switching that I could get clean tones to overdriven tones to it. (I have a layout for it also) I added a spst to switch the NFB on or off. In the off position, it was far more overdriven.
FWIW, my understanding is that Roy Buchanan often played a Champ mic'd thru a PA system. Neil Young reportedly plays a 5E3 Deluxe with 6L6's. Jimmy Page has played all kinds of amps from Supro to Marshall.
With respect, Tubenit