Help with brakes please.

I believe that is a distribution block as opposed to a proportioning valve. It has a sliding piston to cut off front or back braking systems in case of a loss of fluid in either system. The electrical connector on the top is for a warning light on the dash.

I had a locking problem, but it was a bad power booster. Some calipers have pistons that stick, especially those Kelsey Hayes four piston type. I don't think going to a power setup will cure your locking problem.

I don't know how the power brake setup is on a 65 model, but if using a dual reservoir MC and booster, I'm sure new engine bay brake lines are required. I made new lines for my 67 and being the first time, it took a lot of practice to make some good flares on the tubing and finding the correct nuts for the lines as there are several different sizes involved.

As far as the lock up problem, I noticed that if I tapped the brakes after it locked up it would release them. I started replacing brake components one by one until only the booster was left. I never thought of the booster as it was a rebuilt unit installed about three years before. The problem was the push rod from the brake pedal to the booster. It broke off it's attachment inside of the booster. I'm lucky it didn't completely fall off!