After the final fitting of the coolant reservoir, I welded the mounts into the strut tower.

The next step was to plumb the coolant inlet through the firewall. 

Some test-fits

I made this aluminum o-ringed plug on my lathe.  I need to make a large enough hole to pass the flare fitting through the firewall, so I can't use a regular rubber grommet.

.780" hole drilled, which should be large enough to clear the 11/16" hex on the flare nut.

There is an O-ring and retaining ring on the inside to hold everything in place.

Back to bondo!  I laid a coat of Evercoat Tiger Hair, I should be spreading regular filler this weekend.