I tried to edit my original post but couldn't figure out how.
ScubaBob is 100% correct: the thread size on the L&M filters for the Sola 4000 is 37mm, not 35mm as I originally stated.
I'll hunt some more, and test the concept underwater when I can!
EDIT: Just ordered two of the B+W 37mm #25 Red (090) MRC filters from B&H @ $30US each. They say 6-8 weeks delivery - I hope they are overestimating...
EDIT #2: Just a thought - if I locate and set up on a subject using the red filters there may be a possibility that the the camera's white balance won't give enough correction - I'll need to try it to find out. Here's another thought: if the red filter is too red, the filter holders rotate on the Solas, so I could rotate them out of the way with the camera running. That way I might get some few seconds or so of usable video - after I previously white balanced with the unfiltered lights, of course. Still trying to think of more ways to complicate my fun!