I would try capacitor values between 500pF and about .01 mF across the Output of the Reverb Pan (From the back of the amp, the RIGHT side of the pan).
Now, there are a number of updates to the design since the first amps were produced. We will update any Superfly to current design standards for $100 (you'll have to send us the chassis).
Now, if you wish to take the chassis out of the cabinet, I can give you some guidance on how to make a few changes. This I can do in real time, via email.
Next day I received a reply (opposite). I didn't really want to start adding components into the circuitry or making changes as per paragraphs one and three, my knowledge of electronics being sparse.
However I was interested in the second paragraph which mentioned an upgrade service. $100 seemed affordable... except that I was in the UK so shipping it overseas would be expensive.
I sent another email to try and understand what my options were - see part 7.