Thanks for all the replies to my question. I think JoAnns , Hobby Lobby, or perhaps Amazon will have something good enough. I tried contacting SMS several times with no response whatever. I don't need to do business with a place like that.
The dual heaters were an option and I think Model 56. Exploded diagrams are in the parts books. The 47 coupe I had in the 60s had a single heater on the passenger side. The defrosters were not very good.
Under my "aftermarket" seat cover is the original, untorn upholstery.