Firewall Insulation Pad (best plugs to retain???)

I've been TRYING to install a firewall insulation pad in my '57 Nomad. The clips/plugs that came with the REM pad are made of *plastic* (hard plastic) and are made *similar* to the originals, BUT I've been unable to get them thru the holes in my firewall. I've installed original type plugs (long ago - 30+ yrs ago) without issue, but apparently these are no longer available and the REM repros are *essentially unusable*.

There are some 'rubber' plugs available for later year GM products (not sure if hole size is the same, but I suspect? it is?), but these plugs are also made differently and are different in appearance where they protrude thru the firewall. Do they work? or do they leave the pad 'loose'?
Originals were made like this, but worked better. This one is stated to be for a '62 Nova, but not sure if the hole sizes are compatible? or more pliable than the REM pieces I have...?

Attachment 10344
These are stated to be made from 'rubber' and more pliable, and are stated to be for 'GM products from '55 to 81', but they may not hold the pad tightly to the firewall, and are obviously made different ...
Attachment 10345

Has anyone found a solution to this problem? Or have any comments about the above parts?

Hi BamaNomad,
I had issues when I did my install. I ended up chasing the holes with a drill bit (found the largest hole, and made all of the others that size). The first set of plugs were hard (Ecklers, I think), and I ended up getting some others from Danchuk or Cars, Inc.; I can't remember which ones were the best, sorry, but there was variability in the plug properties from different vendors. I sometimes used the driver tool they sell for the plugs, and think I had to grind it down a tad to make sure it didn't immediately blow out the tip of the plug, and sometimes used a carriage bolt as my driver when that worked better due to constricted space. Used a hammer to drive them home.
Regards, Doug

BelAir O ... Yes, the PROBLEM is the hard plastic plugs themselves. I've tried every trick/technique to get them in to no avail... heating, modified a screwdriver into a tool, used lubricant... etc.. but I don't want to remove paint from the firewall to get these crappy plugs installed. I ordered some 'different' (Rubber) plugs yesterday.

I would think there would be an off the shelf alternative at an auto parts store. Seems like I've seen a whole display of different styles and sizes of 1 or 2 piece panel clips.