Tub valve leaking

Maybe the hot valve is 57 years old. I can't find proper washers.
i got a two valve T. One problem I have, the shower head will start dripping with the tub
filling. Water pressure is 60 Lbs. I could replace the t with a three valve and that would fix that problem.
OK, I'm considering a single handle system. That would place it higher up, and I foresee major dripping from shower. Is that right?

Whatever valve you choose, their is a minimum height that the shower head must be from the valve. Consult the manufacturer for that information.

Another thing that will cause the water to be coming out of the shower head while the water is coming out of the tub spout is installing the valve upside down.

There is no reason why the new single handle valve would have to be "higher up", and if it is installed properly there is NO problem with water coming out of the shower head when it is not wanted. What kind of faucet do you have now that washers are hard to find for it? Maybe you need a new source for the washers, because a 1950's valve should NOT be "outdated".

Higher up, I was referring to the valve being closer to the shower head making the water level higher.
That would be nice to know the brand. The washer is not flat, and all I have are flat washers.
Besides, everything is banged up. Patched up, glued up. Need to redo. I would like to have
some temperature control, when I flush the toilet.

Current requirements call for an anti-scald technology in a shower valve, and it's a good idea to update to that. There are two general types, pressure balanced and thermostatic. The thermostatic is nice because you can always leave the temperature setting alone and only adjust the volume. With almost all pressure balanced valves, you do not get a volume control, and the single-handle does double duty: on/off and temp.