Re-gauging trolleys?

There are probably some museum people here who can answer this. There are quite a few examples of broad gauge trolleys from systems like Philadelphia and New Orleans being modified to run on standard gauge tracks, like the ex-SEPTA PCCs now in San Francisco and the Perley Thomas cars from New Orleans that now run at various museums. After a recent visit to San Francisco I'm wondering what this entails. Can you simply install a standard gauge wheel set into the existing truck frames, are the broad gauge wheels relocated on the original axles, or does the whole truck get swapped out?

It depends on the car, and primarily the type of traction motor. If the motor fits on a standard gauge axle, the axles can simply be switched out. If not, modifications are in order. Most wheelsets are integrally cast, so moving wheels is quite difficult.
The objective is to keep the cars historically accurate by keeping the original trucks and as much original equipment as possible.

Thanks; that's the sort of info I was looking for.

Some wheels are pressed on an axle. I’m sure a press could move the wheels inward. The other issue is the design of traction motor, and where the motor support bearings are. Worst case new axles can be turned on a lathe.