[Yukon Jack]

The majority of the thickness you are seeing there is the aluminum plate. It is probably twice as thick as the firewall metal.

Thankfully I had the pedal assembly out when it was time to drill it, I'm not sure I could have drilled it with the pedal assembly installed under the dash, unless I had one of those 90 degree drill fittings. Pretty tight confines under the dash as you know.

See the rubber dust cover on the clutch rod - see where the black material is on the rod to the left of the rubber dust cover - I have black electrical tape around the rod at that location. From the left edge of the tape to the end of the hydraulic clutch master is the total amount of travel that was necessary - it can't be more than about 1 1/2".

Because of the ribbing on the interior side of the firewall and the way the rod needed to attach to the pedal to get the necessary travel without binding, I'm not sure there is any other location where the clutch master could have been positioned.