Have you attempted to install your vacuum booster yet? If not, be warned that the C3 Vette steering column support bracket is different than the power brake support. I have no earthly idea why Chevrolet did that. Besides having to cut a different hole lower down in the fiberglass firewall for the vacuum brake booster location, you will also find that the bolt pattern isn't anywhere near what you need for the bottom two mounting points. The top two MC mounting studs can be extracted, which then at least places the top two vacuum booster mounting points in the correct location, but then you find that the lower two mounting points will not correlate properly with the manual brake spec steering column support structure (which is what the C3 Vette vacuum boosters essentially bolt to) (besides the fiberglass). I checked out a bit of your build thread and see that you are a competent fabricator. I recommend you pull the manual brake steering support structure out and weld in some further material at the bottom of the bolt pattern to properly support the bottom two fastener points of your vacuum booster, OR swap in a factory C3 power brake spec steering column support bracket.
This why we developed a special direct bolt in C3 manual brake spec conversion system that accommodates the different manual brake firewall and the different manual brake spec steering column support bracket:
http://www.hydratechbraking.com/C3Co...920161312A1BD0
Rest assured that I am not sales pitching you on a hydraulic brake assist system, just covering the bases on converting a factory manual brake C3 Vette to a power brake (bizarre why Chevrolet did that)...
