You might not want to do that foot switch conversion..... The reason being, is the normal way to go triode/pentode is to connect the screen grid to the control grid, while disconnecting the screen grid from the high voltage screen grid supply.
Normally screen grids have about 5-10 percent less voltage on them than the plates. Control grids have about 75 AC volts on them (AC signal riding on DC bias of some negative voltage... about -45volts to -55volts).
I dont think we want to do that... in a remote switching arrangement.
The "better way" (safe way, non-noise way) is to put a relay in the amp, have it do the switching, and control the coil of the relay with your footswitch.
Keep in mind - and I've not heard the Blackheart... only others with TP switching - that when you flip the switch*, under load, it makes a loud pop, unusuable for stage switched use.
*not to be confused with ACME Truck Battery Co, Inc's "Flip the switch and start the bitch!" ad copy.