Subject: 1974 front disck question

OK,

I have to replace the fork dampners in a 74 LAPD disk. Im gonna put
stock dampners and progressive wound springs.

What gives with the PVC insert I have seen commented on this site?
I did pick up some thin washer like devices from Ago's last year but Id
like to know more about the PVC insert and if I should do it.

Thanks a bunch

Scott