1966 GMC Brake Booster adaptor
 

1966 GMC has 3 countersunk fasteners that hold the tapered plate to the fire wall. Looks like on chevrolet's they have 2 existing bolt holes and you have to drill 2 more. My question is do they make an adaptor bracket with the 3 countersunk holes to use for the booster upgrade. 1st picture is my fire wall 2nd picture is the original tapered bracket that attaches with the 3 countersunk holes. The brake mechanism attaches to the 4 threaded holes in the tapered bracket.

Re: 1966 GMC Brake Booster adaptor
 

I need to learn what you are asking. What exactly (part number and vendor) do you mean by "the booster upgrade"? I may or may not be able to help you. Others know more. But for my own education.
1. I assume the truck had PS and you show the "adaptor bracket" for a booster, and then a MC was mounted to the booster.
2. I assume you want to buy a newer booster and MC? But the new bolt patterns don't match the old adaptor?
3. I assume you are asking if there is some sort of other adaptor that will work with some new parts you have.
4. If I see more pics of the old and new parts, I can suggest a fix if no one here knows of an adaptor.

Re: 1966 GMC Brake Booster adaptor
 

Give me a few days, i'm doing the same upgrade to my '65 this weekend... we can compare misery