Hi Bill - the idea for a carbon tissue utilizing silver halide instead of dichromate UV depends on a hardening action to occur, either when developing in a pyro developer, or using a bleach as in the old Kodak Wash Off Relief process. You would want to verify if either of these two image hardening techniques will work with PVA. The next thing to do is to determine how much pigment you need to get a good DMAX on the print. You would want to make up four types of 'tissue' (I would coat on mylar myself) : Cyan, Magenta, Yellow and Black. The pigments themselves will absorb the exposing light, giving the light penetration limiting effect. Exposure is from the emulsion side, unlike DT. The $10,000 question is: if you put in enough pigment for a good DMAX, can you still expose the emulsion? If speed is too slow, you could always formulate a faster emulsion. I don't think grain will be much of an issue. My guess is that it will work, since the absorbtion of the pigments will be similar to the dyes in Cibachrome, which has a decent DMAX - a slow speed, but usable.
Regards - Jim