I just put a set of used coupe deluxe rears in my convertible to see if they fit and they look like the same widths to me.I have standard interior and i do see a difference (maybe i'm seeing things)between my standard and the deluxe in the depth's of the seat uppers.The deluxe seem to be shallower than standards.The bottoms seem identical in measurement.Camaro's are different i believe,like Dave mentioned about the armrests.I believe Camaro standard interior rears were wider as there were no armrests and deluxes were not as wide as they did have armrests.Maybe the shop guys are mistaking your car for a Camaro lol

David