Suggestions for fast on-location callibration?

yes, defintely, whitebalance both cameras on location. This will get them pretty close on White-balance. Are they the same make? if so, will probably be better.

Exposure - well different cameras tend to meter slightly differently, but you'll just have to get used to this if your two cams do meter a little differently. In any case, brightness differences can be easily rectified in post-production when you get the footage onto a PC.

I'd keep shutter speed the same, and aperture and gain similar too.
Both on Auto will probably do, or you can put both on manual.
It's going to take a little experimentation onyour part.
I would have both on monopods or tripods too. just try to minimise differences between the two. And then there's the audio .....