The M3 has two flash connectors. One for x-sync and the other for m-sync flashbulbs. And you can actually use both of them at the same time. So I did an experiment with color infrared film in the camera, a Graflex reflector with a #5R infrared flashbulb, and a modern Canon electronic flash. This actually all worked out at the basic technical level: the electronic flash and the flashbulb fired and their light output was fully recorded on the film. Unfortunately I didn't quite get the desired result as the IR flashbulb had a much stronger effect than intended.
I'll probably experiment with this again some day...