Thanks for the input. I’ll share that information with the owner the next time I see him.
After an hour or so searching my computer files, I came to realize I lost all my dimensional drawings and specifications on the earlier diamond tufting work in the hard drive crash a few years ago. Fortunately I recovered the foam and backer dimensions by removing one of the small end panels behind the seats and measuring the diamonds on the back side. I was equally lucky finding a piece of trimmed scrap that had the full markings showing the exact dimensions of the fabric, which provides for the tuft allowance:
All those dimensions are now loaded in a new file on my hard drive, as well as the back up drive, along with a hard copy print out (just in case).
I also determined which direction the fabric stretches and which orientation is required to have it stretch correctly on the seats and door panels. In my case the vinyl fabric stretches across the width of the roll, so the length direction of the fabric must be laid out from left to right across the door panel, so the stretch provides for the correct vertical dimension of the diamonds.
For anyone interested, my tufts will be 4 ½” high x 3” wide on the foam and backing, and 5 1/8” x 4” on the fabric. They are much smaller than most traditional diamond tufting, but this smaller pattern was very popular in the late 60’s, and I like how busy it looks. It’s also about a hundred times more work than larger diamonds. If I didn’t already have so much of it finished that would have to be done over, I’d probably switch to larger diamonds just to make it easier.
I then laid the pattern out on the seat foam to determine where and how many diamonds and buttons to apply. I can now visualize the seats being finished:
Between yesterday and today I picked up the foam for the seat tufting, and the ABS sheets and glue for the door panels. Luckily I located my commercial quality hog ring pliers & hog rings. I think the only thing left to pick up is a few more yards of matching marine vinyl. If everything goes well that will be in hand by tomorrow afternoon, and I can get started on the actual tufting process in the next day or two.