Nice. If you open it up there are some little board mounted trim pots in there for the reverb and chorus. I tweaked mine a bit. I suppose it should be possible to wire some panel mount pots to those locations. Somewhere I have the service schematics for the early 250ML that might help.
Yeah I know about those. You can also adjust the amount of gain for the gain switches. The bad thing is that one or two of the other pots adjust the bias current on the power transistors and you can get horrendous crossover distortion if they're off or even fry the transistors. I realized this after messing with mine and getting a weird oscillating noise. I then googled and found that I had messed with the wrong pot. I turned it until the noise went away and it still works so I guess I got lucky.