To me, the most important mod on that circuit for Jerry tones is to swap in metal film resistors in the plate positions. The Vishay/Dale 100k 1-watt (or .75 watt is what's available now) is a mil-spec component. This will have a big impact on tone.
For improved reverb, it's important to make sure the tank is the correct impedance match to the circuit. If the tank is the wrong match, replace it with a correct-spec one (MOD makes decent current-production tanks -- get the full-length, 4-spring, long decay style at the correct input/output impedances). Also verify that the reverb components on the circuit board are within spec. If they aren't, replace them with new parts that test out well.
I would also recommend adding a reverb dwell control. This way the existing reverb control will alter only the wet/dry mix of your signal. The dwell control will adjust how hard the signal is hitting the reverb tank. Having these two functions separated will help give you a more controlable, pleasing reverb.
You can accommodate a reverb dwell control either on the back of the chassis, or else disable the tremolo circuit and use one of the open positions on the front panel for a dwell pot. I would opt for the latter approach.
Some folks here might urge you to mod the tone stack capacitors on the reverb channel to what Jerry was known to use. But the Bandmaster Reverb has a fixed-value middle control, right?
Since you have a modded Dual Showman Reverb, I suggest you do the plate resistor and reverb mods first and then see how you like the amp.
and has such a sweet tone and plenty of power with just the right amount of head room.
