What I'd do for a "null" filter to simulate the orange mask is simply use a c-41 processed unexposed
sheet of color neg film - in effect, the whole sheet become the basic filter, then after that try to simulate enlarger values with cc filters. Of course, this can be shortcut with less filters once you know what is needed. I'd rather find the base values in the lab first, with the colorhead adjusted to daylight
using a color temp meter - you'd waste less time in the field that way. ... but excuse me for thinking
out loud ... I've got a lot of calibration work starting this weekend myself with some experimental
techniques with color neg paper. But whatever you do with it, you first have to recognize that it's
engineered with that orange mask in mind. When I'm making black and white printing masks, for example, one has to accomodate the spectral sensitivity of the b&w film to both "see around' the orange mask and for the slightly depressed green sensitivity of pan films, and certain other things too.
This is just to get to first base. Once you get there, the real fun can begin. But color paper is certainly
cheapr than color sheet film at the moment, so I guess one isn't going to go bankrupt trying this!