Blackfacing in a SF Fender guitar amp is a matter of upping the impedance of the PI (phase inverter), changing the bias balance to a bias adjust, and the removal of rf suppression caps (IF there is no oscillation as a result.)
I don't see what the advantage in this amp would be. The preamps are nothing like a Fender guitar or bass amp. I don't like changing the bias balance but would prefer to leave the bias balance and add a bias adjust (replacing one resistor with a pot and resistor.) Why not have both? The purpose of blackfacing was to lower headroom, make it easier to break up the amp, and add some high end complexity.
Tell more about your amp and your goal in the modding?