Since you said all the wheels were locked up when you jacked the car up, the problem is probably not a hose, the hoses would only effect individual front wheels or both rear wheels but not all the wheels at once. The problem is going to be in the master cylinder. Like others have said, the master cylinder needs to return all the way back until the piston hits the snap ring. When you first step on the brakes the piston in the master cylinder moves forward covering a small hole in the bottom of the reservoir. Once it is past this hole the piston can start increasing the hydraulic pressure in the system. When the pedal is released the piston returns and uncovers the little hole so the fluid can return to the reservoir. If it does not uncover the hole the brakes will stay locked up. You need to have a little free play in the brake pedal linkage for this to happen. Remove the rubber boot from the master cylinder and see if the piston is returning all the way back and is seated against the snap ring. There should be no fluid leaking out the rear of the master cylinder. Check that you have a slight amount of play between the rod and the piston. If you do not have any play check that the rod is adjusted properly, the linkage is not binding up, grease the pedal bushings and check the pedal return spring. If this is all Ok you have something plugging the return port. This is probably rust laying in the bottom of the reservoir.
I went to a Bendix brake seminar and the instructor said that if people would change their brake fluid every two-years master cylinders and wheel cylinders would virtually last forever. Brake fluid is hydroscopic, meaning it attracts and adsorbs water, up to 2% or 3% per year. Once this water is in the system it causes the cast iron wheel cylinders and master cylinder to rust which pits the cylinders causing fluid leaks, the rust particles are abrasive so they wear away at the rubber cups, also the rust plugs up the little fluid ports in the master cylinder.
Take the cap off your master cylinder Check, the master cylinder cap gasket, if it's bad it will allow moisture and oxygen into the system causing rust. What color if the fluid brown or red indicates moistre has gotton into the system. If the brake fluid is black this is an indication that the rubber cups are failing and the master cylinder should be rebuilt or replaced. Your problem could be caused by a small piece of a rubber cup that is plugging the return port. Remove all the fluid, wipe the crud out of the bottom of the reservoir. Make sure the little return port is open. Fill the reservoir up with fluid and apply the brakes several times, Remove the fluid again from the resevoir if its still rusty. Repeat this until the fluid is fairly clear. Fill it back up again and flush all the fluid out of the entire system starting with the right rear wheel, then the left rear, right front and finally left front.
Another problem with collectors cars is they sit for long periods of time, the worst thing you can do to a car. The master cylinder has a residual pressure check valve which always keeps a slight amount of pressure in the system. This keeps the rubber cups in the wheel cylinders pushed against the walls of the cylinders preventing brake fluid from leaking but it also prevents moisture from entering into the system. Moisture cannot enter the system if the pressure in the system is higher than the atmospheric pressure. If a vehicle sits for awhile that residual pressure will bleed off and allow moisture to enter into the system. Even if you do not drive your car you should stomp on the brake pedal once in awhile just to keep that residual pressure in the brake system.
