Easy and inexpensive
Mark, the conversion is relatively inexpensive, and very easy to do. Replacement vacuum boosters are available from quite a few suppliers for around 280$. The only other items you will need, are a front left distribution block, and a vacuum fitting for your intake manifold.
If you decide to go for it there is also one more recommendation I would like to make, and that would be to also replace your single m/cylinder with a double reservoir model. Don't even think about finding one for a 65-66 model, because we both don't earn enough money in a week to afford one. What you do is go down to your local "Auto-Parts store" and ask them for a rebuilt m/cylinder for a 67 Corvette power brake model. They are available from most of the rebuilders such as " Wagner ", Raybestos, etc, and usually are sold for approx. 30$ without a core.`
While you are there, you should also bring with you your old distribution block , which has four holes, and ask them to supply you with one that has only three holes in it. They sell these for about 3$, and the Corvette resellers have them in most catalogues for about 35$ to 40$.
The only other item you have to find, or make is a small flat metal brace that is needed to bolt the upper booster bracket to the firewall. This brace is found on all cars that came from the factory with P/brakes, but not used on a standard brake car. It is actually a flat piece of metal about 1" by 6" in length, that has two holes for the rivets to mount it to the dash, and another two holes that have embedded nuts, into which the upper booster brackets are bolted. This brace is installed under the left side wiper grill, and is bearly visible when the grill is in place.
Except for the lower booster mounting, the rest of the conversion is rather straightforward. Remove the old m/cylinder, and distribution block, install the vacuum booster to the dash, bolt up your new M/cylinder after having bench bled it, and bolt the distribution block to the frame, and hook up your vacuum and brake lines.
The only problem you will have is with the lower mounting bracket on the booster. This is how it goes together, and another easy way to solve the problem. On a non/power brake car, there are two bolts protruding from the lower pedal bracket through the dash, onto which your m/cylinder is presently bolted. On a power brake car, these bolts are not used because the lower braces on the booster already have two studs welded to the brackets, that go through the dash and bolt to the pedal bracket, with nuts from inside the car.
In order to be able to mount the booster, these lower to studs must be removed from the pedal brace. Not an easy thing to do because they are press fit with splines in the bracket, and are very hard to remove when the pedal bracket is in place. No amount of hammering will loosen then from the brace, unless a very firm backing is provided from the under dash area.
A much easier solution can be found by leaving the original studs in place, and just removing the studs that are in the lower braces on the booster you will be purchasing. Before the booster is installed, these studs can be easily removed, and then the booster can be fastened using the nuts that held your original m/cylinder in place. Not NCRS for judging, but a h-ll of a lot easier to accomplish, then doing it by the book. Hope this helps, P-Me is anything is not perfectly clear.