I was in Autozone looking for a PVC grommet that would fit in the firewall
hole where the plastic fuel line connector lives, and I tried a Dorman
'Help!' piece, part # 42055 (for 'various GM models 1983-76'). It popped
right in, fit tight without movement, and it has a thick inner wall. It
should be available at just about any FLAPS. I thought I'd put that out
there and possibly save somebody some legwork.

Cya,

Robert