63 Riv Upholstery - Help!

[TexRiv_63]

I am new to this forum and this is my first new post. I am starting the process of installing new repro seat covers and seat buns from Clark's Corvair. I am starting on the driver's bucket and before I get myself in trouble I wanted to ask this group for any advice from someone who has already done this install or who knows more about upholstering than me (that leaves it wide open!) My first concern was the trim buttons that are used in the center of the cushion and back inserts. The ones in the seat back are simple push-through-and secure items that look easy to install, but the ones for the bottom cushion are mounted on an elastic band with a small metal piece at the bottom that goes through a heavy piece of cardboard to hold it in place. These are hell to remove and I have no idea how to reinstall them. Has anyone actually done this, and if so how did you do it? Before I punch holes in my new upholstery I want to be totally sure I can get these buttons back where they belong. I would be grateful for any help.