On a 69 fj40 I have the distributor would sometimes move out of position after being driven bc the bolt or clamp wasn’t tight enough. The truck would run fine when starting & idling. The next time I would go to start it after driving it the distributor wasn’t in the same position I had in the day before and the timing would be off. I tightened up the distributor and it stopped back firing when I would go to start it and has ran good since. Seemed like some of the same issues you are having. Or maybe your coil is on it’s way out