In addition to what Dr. Wayne has mentioned, I also suggest measuring the truck side frames from axle-to-axle. If you plan on using the same side frames, this will ensure the new drives fit them.
Russ
Modeling the early '50s Erie in Paterson, NJ. Here's the link to my railroad postcard collection: https://railroadpostcards.blogspot.com/
If you're referring to the motors, I'd suggest that you check out NorthWest Short Line for their Stanton Drives. These are self-contained underfloor motor/truck assemblies, available with several different wheelbases and various wheel diameters, too. You can contact Dave there, and let him know what you have and he can likely recommend the best options available.
Wayne
Hoping there are some trolley people out there who can help. I have a collection of old and new trolley pieces as I can't resist them when I go to the train show exhibitor sales or used hobby shop. I've picked up a few of these old Bowser models, with metal shells and bases but the engines barely work or stop working. Any ides how I coulld replace these engines? This model in particilar is a an old Jewett tandem tram car with live wire option. I also have a PCC car same vintage.