Here's another approach:
I bought the reservoir from a street rod supply shop off the 'Net. Of course, I got it home and then realized that the bracket it came with would not protrude enough off the firewall to clear the throttle linkage. I then reached out to fellow CC member Rob Frink and he (based on my drawings and measurements) CNC machined that neat little spacer that you see against the firewall. Bingo...instant, leakproof reservoir. BTW, this photo does Rob's work no justice, as it's actually a triangular shaped spacer with different depths.
It's been so long, I honestly don't recall where I got the reservoir from. Rob may still have the CNC program to whittle another, but you'd have to reach out to him.
-Dean #747