SMS will provide faster service when you just want material, and they will have the correct material you need or will have it reproduced. You might have to send them emails from time to time to keep them on your fabric order but you should usually get that within 3 to 6 months. They aren't cheap though, but you probably will not find it anywhere else. They are the only real show in town for original, and they take advantage of it. I am told the owner won't hire more people because if he did, he would have to provide health care coverage, and he will not do that. So it is what it is. I would not have them make the seats unless you really want to wait a long time. They just don't have the staff to deal with all the business they could do if the owner wanted to.
I would also get new foam from your reupholsterer - they can cut it to fit using an electric knife usually. You won't find moulded foam for those seats more than likely.
I am an original guy, and don't see the purpose of buying an older car to drive and them put modern seats in it. People just tend to put an old car down when they see things like that. But you may not care - it is for your enjoyment.
Good luck.