Hi guys, I don't know whether this will be of any help to you, but I have had practical experience with the Ham Std Hydromatic props in the past - having worked on them. I have none with the Curtiss prop, but I have a basic idea of how it works. Both use different mechanisms in their hubs to achieve the same end.
The Hydromatic prop relies on differential oil pressure acting on a piston located in the dome out front, hence why its so big, to change the blade angle. This works by the supply of oil from the governor, which 'senses' changes in engine rpm and consequently allows oil to flow through the prop shaft to a distributor valve in the hub. It doesn't require any further controls in the cockpit, apart from the condition lever (propeller pitch), which is a "master' control for determining which blade angle range to use at which engine power setting, which is controlled by the power lever, depending whether the aeroplane is on the ground or taking off or cruising, or what have you.
The Curtiss prop, the action is all electric. The smaller hub has a speed reducer forward of the blades and an electric motor ahead of that fitted with a speed brake. The governor does the same job as it does on any aeroplane, but it sends electrical signals via a relay to the prop, which is fitted with slip rings on its shaft. these generate power via brushes which drives the motor, which in turn via the speed reducer, a mechanical device, converts the speed of the rotation of the prop to alter the blade angle. The switches in the cockpit also connect to the prop via the relay box. Their function is to configure the prop as either fully variable pitch using the condition lever and governor set up as installed in any VP equipped aeroplane or to set the prop at a fixed angle by shutting off the electrical signals to the governor. In effect this produces a fixed pitch condition, which can be over-ridden, but would be used during cruise or lengthy climbs and to feather the prop if necessary. On Ham Std props, feathering is also done electrically. Nominally however, with Curtiss props, the use of the condition lever was the same as any other aircraft.
As for interchangeability - and I'm only guessing, the wiring would have been installed at the factory and instead of removing it to fit a Ham Std prop, it is most likely that it was terminated and left in situ and the cockpit switch panel was removed and the space blanked over. Glenn, if you look on the back of your switch panel, you'll see that the wires connect directly to the switches; removing these would be no problem at all; its something we do at work all the time, although these days, switch panels are connected to the aircraft wiring by cannon plugs, which make life easier, - it means you don't have to reconnect wires every time you change a box.
Alternatively, the wiring could have been removed, which was quite possible in the field and it wouldn't have been a big task, although it might have been a bit awkward given space limitations. Just removal of the wiring itself, the relay, the switch panel and the prop. The governor wiring would stay in place if the aircraft has a feathering prop, although not all single-seaters had these - blade angle range determines that - but it wouldn't be too much effort in the field.
Like I said, these scenarios are guesses, but are most likely. I've heard of Ham Std props substituting Curtiss Electric ones on other types during the war; the early British Liberators, specifically the Lib Mk.II was built with the Curtiss prop, but those ones diverted to the USAAC were retrofitted with the Ham Std props. A number of P-40 owners today have fitted the Ham Std prop to their aircraft rather than the original Curtiss prop - simplicity, I guess. Parts might be another reason to do it these days.