I got out my Campy SR and Shimano 600 levers today and tried swapping hoods. The Campy SR hoods will fit on the Shimano, but the latter have just slightly longer reach in the body (lever is a bit farther from the handlebar seat; they'd probably work okay, and they fit around the cable horn and the front opening well. The Shimano hoods have a molded shoulder inside in the area where the cable exits the horn, and they won't fit onto the Campy SR lever bodies. One significant difference between the Campy SR bodies and the Shimano 600 is that the latter require an aluminum bushing to stop the cable housing, while that's integral to the Campy.

I noticed a weird thing: the Campy SR bodies are not completely symmetrical around the bottom of the handlebar seat; one side droops down farther than the other (the left side is lower, when viewed from the rear). I thought that possibly they're "handed" and that I had two from the same side; but I got another pair today, and all four lever bodies have the same "droop".