EZ, have your friend look here ---
http://paintref.com/cgi-bin/chipdisplay.cgi?year=1966&manuf=GM&smodel=Cadillac&info=&page=15The interior colors are in the second row. Maybe he can identify what he has from there and give his paint supplier the correct color to mix, if they still have the formula. Doubt they can mix dye colors but flex agents can be added to paint to make it more suitable for vinyls using a primer like Dupli-Color's "Adhesion Promoter". SEM makes an adhesion promoter also.
I just finished "redyeing" a dash top for the Caribou from black to dark red using SEM vinyl "dye" and it came out very well.
Geoff