Grommet for Through Pedal Box Hydraulic Lines

[mach'er]

I found this grommet (Danchuk 820, for a 55 Chevy), and ordered one to see if it would work.



Lo and behold, it is almost perfectly sized for the clutch cable hole in the firewall (which I'm not using, since I've gone to a hydraulic clutch):




All it needs is the holes drilled out a hair larger than as delivered.

Anyone have a smart and successful way of drilling/reaming out holes in rubber? I ruined the one I ordered, but it fits so good, I'm willing to try it again.

Or, does someone have a better method of creating a sealed pass through for three reservoir 1/2" hoses (two brake, one hydraulic clutch) and one brake line? I thought this could work great, but am willing to look at other ideas.

Thanks!
--Curt