Does it work when you replace starter? Or still intermittent? If it works at first, are you replacing the bushing in transmission too? If that bushing is worn the motor can fail. If it works intermittently with new starter you need to check ignition switch and wiring. What starter are you buying? There are some low priced imports but I don't know if that could be a problem or not.
Perhaps this is an obvious question but the 65 is a 6V vehicle. You are putting in a 6V starter, right? Sorry but I have to ask
The wiring is always a good place to look for problems, especially for a 6V vehicle. The ground from the battery to the body, next to the battery, must be really good. The ground strap from the underside of the body to the transmission must also be really good. It is easy to forget there is a ground strap under the body.
A good, safe, test is to connect a voltmeter from the negative terminal of the battery to the housing of the starter. Have someone look at the meter while you crank the engine. I don't remember what the maximum voltage drop should be but if it is over 1V, you probably have poor grounding in the path from the battery to the starter. If you have a really long set of jumper cables, connect the black jumper cable wire to the ground post of the battery and the other end of the black jumper cable to the starter housing or some part of the transmission near the starter. Then try cranking the engine.
Second thing to do is connect a voltmeter from the positive battery terminal to the starter battery terminal. This will measure the voltage drop across the positive connect the red jumper cable connector to the starter's battery connector. Same test as for the ground wire. Should be less than 1V.
If the battery grounds are in good shape and the positive power cable is ok the last thing to check is that the solenoid is getting a good amount of power from the ignition switch. Have you tried cranking the starter from the starter contacts themselves? PUT THE CAR IN NEUTRAL, SET THE PARKING BRAKE and block the tires (you don't want the car running over you or someone else!). Make sure the ignition key is not in the ignition switch. Either jump the large starter power cable to the small solenoid using a screwdriver, or for more safety, hook/clip some large wire (14 gauge for example) that reaches out from under the car to the two starter terminals and touch the other ends together briefly. The starter should crank every time. If you are not comfortable doing this type of testing, try this: get a long 14 or 16 gauge piece of wire, maybe 6' to 8' long and put a "fast-on" type female connector on one end. Remove the small solenoid wire on the starter and hook your long wire to the starter solenoid. PUT THE CAR IN NEUTRAL, SET THE PARKING BRAKE and block the tires (you don't want the car running over you or someone else!). Make sure the ignition key is not in the ignition switch. Take the other end of that wire and touch the end to the battery positive connector. The starter should crank every time.
If the engine cranks every time, the problem is likely in the ignition switch itself.
If the car runs ok once started, then the power wiring to the ignition switch is good. The only things between the ignition switch and the starter solenoid are the crank contacts in the ignition switch itself and the wire that goes between the ignition switch and the starter solenoid. I have not seen a bad wire before.
This should help isolate your problem. It still could be a bad starter but you have already replaced it at least once. Let us know how these tests turn out and if you found the problem.
I am red faced from embarrassment. My battery was not in as good shape as I thought. It was the culprit after all. I’ll blame it on being distracted by my 4 grandsons. It’s a full time job keeping their trikes , bikes,
4wheelers and such going. Thanks for your time.
I would not get too embarrassed as discovering it is a bad battery is often overlooked. I have seen quite a few batteries that tested ok in most all tests that were actually bad. Generally it is when a very high load is applied, like when cranking the engine, and the plates in the battery flex and short. I see this more on V8 engines so did not think to put that in my list of questions. Great you got it fixed.