What glue are you currently using? Most use weldwood landau glue. Its yellow in color but when applied lightly on thin material its not normally an issue.

I've had good luck with the Fisher silver space pens. I tried out some of the cheep refills off of ebay and had a hard time getting the ink off of some materials. Also had issues with the ink leaking out of the refills when they were just sitting around. The Fisher pens cost more money, but they last a long time and I haven't had any issues getting the marks off.

Ahh got ya, I figured it had to be something like that

Now I'm curious, what is the significance of it being 1 1/4?

I have bought some of their seat medallions from them in the past. Always shipped quickly and where great to deal with.

This might work for you
http://www.kristkustoms.com/brushing.html

I actually just spoke with my foam supplier about this yesterday. They said at this time they didn't expect an increase in cost anytime soon. She did tell me that one of the chemicals they use to make the foam was going to be in shorter supply than normal though. I'm in the United States.

For just general cleaning and for removing marks from space pens, china marker, and chalk I use Chemical Guys Nonsense cleaner. https://www.chemicalguys.com/nonsense-all-purpose-cleaner/nonsense-cleaner.html I really like it and haven't had any adverse effects from it so far. To remove glue and other difficult things I use Malco Cosmoline Remover. You need to be careful with it and try it on a test piece first because it is a solvent. https://www.malcoautomotive.com/A___L_Cosmoline_Remover-details.aspx

Don't plan on ordering anything from ACC. I tried to order carpet from them last week by the yard and thats a no go. At the preset time they will only sell you 1 yard. They are worried they are going to run out of material to make their carpet kits out of. I'm looking for alternatives myself.

I did a bench seat for my personal C10 last fall and tried this method out. I used the stock seat frame and put 3/4" plywood for the base and back rest. I used 2.2 density 50lb compression foam on mine and shaped it myself. It was a little on the stiff side when I first did it. But after you put some miles on it the foam seems to break in some and get softer. I'm pretty happy with it, but I wanted the firmer feel and never liked how old truck seats can be a little bouncy. I'm not sure what the density and compression is on the Snowden foam so that might make it feel a little different. I've see quite a few guys do it the way Justin mentions also with cutting out the wood under where you sit and weaving jute webbing in that area. I was going to try this method out on my next one.

My helpers usually claim the old seat covers.