I finally got my package of cling vinyl today and discovered that it is
indeed the stuff the vinyl open-reel tape retention strips were made of
in the days of yore.
The stuff is Grafix-brand "Cling Vinyl", KFC9-ASST. 9 9"x12"
paper-backed sheets. Easy enough to cut with scissors or standard paper
cutter. 6" long x 3/8" wide seems to be about right.
No more foam blocks!
--Chuck