If i understand correctly you want to use the original outer leather band and sew in a new insert.
So if your using the original insert as a pattern you don't really need to change anything on the insert.
Just sew the outer band 1/16 or 1/8 past the original sew line. That tiny bit is not enough to make a large difference when putting the cover back on.
If the outer band had a top stitch i would still sew past the top stitch holes about a1/16
So in if the seam allowance was 3/8 now its 1/2 inch.
You could add 1/8 to the insert but not necessary.

Not sure if those seats have an airbag deployment seam. If they do we can help sew that with a Docusew.
If your making them from scratch.

I would reach out to Wyotech. The students come out with a good foundation. Yes they will need more training but it's an option. Unfortunately good trimmers are hard to find. Average ones dime a dozen. We dont seem to float around like paint and body guys.

I don't like them at all. I like using washable crayola markers. The fine tip.

What are you asking per book?

I thinking like 100 yards.

Another helmet done for a upcoming charity auction.

I think he only sells supplies and uses a local upholstery shop to do his seats.

Caddilac with Factory kustom look.

I so use a variety of markers but I just started using Crayola ultra clean washable markers. Best thing I have found for marking anything. Washes out pretty easy and so far no bleed through.

I turned my foam saw to a bandsaw. I just drilled four holes tho the base plate that comes with the saw. Then attach that to a table. Works great with long cuts. Others have a little different set up.

Old chopper seat that has been reworked. I wanted to make it look like a over the top boot.

I use acetone haven't had any ill effects yet.

Yep I learned a lot from him technically but as far as design he is on Tesla level.

Yep semi retired comes out once in a while to show he still got it.

Diamonds last forever or so it seems. The next insert craze who knows. I just know now that there some suppliers that will computer control Stitch any design you can come up with. Which seems the way to go now. I am a fan of the cloth designs from the 50s and 60s. I wish the cloth was more available from suppliers and customers open to use it.

Helmet I did for a local charity event.

I do the same. I
If I don't have a wheel I just use a single needle and make the holes. It takes a little longer but works.

Keystone sells one that is flexible and I like using.
Not sure what its called.

H3 Hummer seats. Not too hard to do but definitely had to trace a lot of lines. Making a stencil was a key to get it done quickly.