Lots of good ideas here. Thanks to all for chiming in. Sounds like the dichroic filters will allow too much light through at any setting for this to be a workable alternative to a true red filter. I might pick-up some red posterboard and try the aforementioned idea regarding marking and positioning.

Curious, though, why Ralph Lambrecht suggested maximum cyan as an option. Given that orthochomatic paper is blue-green sensitive, I (and others obviously) wouldn't have thought that would work. But he's written extensively on analog photography, so he must know something I don't.