For the brakes, if you used the original brakes they should work as well as before. If the rear locks, it may be the proportioning valve, and you should be able to swap in a v8 unit or adjustable unit If it is the front, check that the calipers are not sticking. If they sat for awhile on a donor car, the pistons may be sticking. Make sure the calipers can float. If you had air in the system, you usually have little or no brake actuation at all.
Also make sure the pushrod from the power booster to the master cylinder is adjusted to the right length. If it is too long, it will apply the brakes, but not allow the brake pistons to return far enough to open the return ports. If you swapped to manual brakes make sure the pedal to m/c pushrod is on the correct linkage mount on the pedal.
For the carb, see if it has obvious leaks when sitting there. Most likely it has a float level that is too high in front or rear, and is draining when shut off. With the engine off, look carefully down the carb throats and see if you see gas. If so, try lowering the floats. It takes a 5/8 wrench and a wide screwdriver. I cannot remember which way lowers right now. Loosen the screw a bit, with the engine running, and turn the nut, with the bowl screw out of the side, until gas just barely runs out, or does not run out. The nut is the part that raises or lowers the needle and seat assembly. That should do it.