Mikeg103 I go to the fabrick store buy a canvas type material that is kinda stiff,my wife can sew that so the joint wants to be L shaped,use your old cover for a pattern,on a 51 3100 that cloth is held with clips that don't hurt it like hog rings. Change out weak springs,pad with new foam tied in place so it wont move. on beaters if it wears thru you can turn it inside out and go some more,like on a wood hauler. Make you some cardboard patterns of seat top and back to work off of they are easily changed !!
I used the covers and backing material from Jim Carter. The quality of the products was very good. I had read in other posts that some people put down carpeting instead of the batting. I had the batting from the kit and wanted to use it. I also liked the idea of separating the springs from my backside. I ended up getting a very thin, vinyl backed carpet runner from Home Depot. Combining the batting and the very thin runner worked well.
In the attached pics, you can see a comparison between the original "V" shaped clip and the replacement weird shaped clips. By wrapping the cover around the frame and tucking it into the groove in the frame, you can replicate how GM did it. I'm including a pic that shows the frame sitting on a piece of gray carpet. In the pic, you can see the cover wrapped around the frame and a spring clip holding it in place to the left. Additionally, you can see the bends in the fabric where the permanent clips were installed into the frame, holding the fabric cover in place. The third pic shows a close up of the clip, in place.
My truck is a 1953 3100, so I chose from that group of seat covers. I know it is the spanish grain version and think it is the brown color, although it may be the maroon. I honestly don't remember. It looks more brown in the attached pic.... If you have a remnant of the original fabric, I'd use that for color choice. I found a ton of the original fabric embedded in the channel that the clips fit in. In fact, it was very tedious getting it all out so that I could reupholster the seat! The second pic shows the frame with the replacement batting and burlap sitting in place, but not attached and also shows the groove and original fabric remnants.
mike 103 I go get kinda stiff canvas material ,my wife sews up covers I put in strategic springs pad it clip em on there,head for the woods. That is on a beater !! Also make a cardboard headliner,about every 5 years