If a band adjustment doesn't fix it here are some other thoughts.
Since it's happening after it warms up (when the fluid has warmed up and thinned out) it's likely the primary cause is too much fluid leakage past the internal seals inside the drums and/or servos. The only way to actually fix that is new seals which means a rebuild. But before you contemplate going that route there are a couple of things worth trying. It's possible it's just a misadjusted transmission rod (between the
carb linkage and the trans) Per the Ford Manual, if you are getting flare you can try to fix it by adjusting the rod to the transmission. Presuming it's already adjusted per the basic spec the recommended adjustment is to "lengthen" the rod. In practice you lengthen it by disconnecting the swivel and unscrewing the adjustment link. Ford Recommends trying 3 turns and not more than 4 turns. I had a small flare occasionally (cold or warm) at low throttle openings so I lengthened the rod 4 turns and it almost completely eliminated the occasional flare. Lengthening the rod increases the internal pressure of the transmission... higher pressure results in more fluid flow to help overcome leaking seals. But you might want to start with checking the basic adjustment and see if your car is where it's supposed to be with that rod adjustment before adjusting it more. Maybe someone has got it out of whack by past miss-adjustments. I only have my own car to go by but here is a suggestion. Before I made the adjustment if I pushed the throttle to the floor so the
carburetor was open all the way, that linkage with the slot would move so the "pin" moved to the center of the slot. (engine off of course). After I lengthened it the 4 turns it moved the pin about half an inch toward one of the ends, don't recall which, but not all the way to the end. So you should check that before adjusting anything and make sure when it's floored the pin isn't bumping into the end of the slot, I'd say ideally it will be in the middle as the starting point. Ditto after you adjust it, make sure the pin isn't hitting the slot end.
The second thing you can do if the adjustment doesn't fix it is something I have done a couple of times over the years for transmissions with leaking internal seals. It helps without hurting anything. Put some STP oil treatment in, the classic stuff that's like honey. Start with one 16 oz can. It's really thick, you may want to heat it in the over to make it easier to pour thru the dipstick tube. I've added as much as two cans of the stuff. You may need to suck some ATF out first if the trans is filled to the top already. The STP will increase the viscosity of the ATF which will help keep so much of the oil from leaking past those worn-out seals.
If none of that works the last thing you can try as a hail mary is a can of Seal Sweller. I don't recommend the seal swellers unless you have tried everything else, I've seen some seals that were turned to mush by them. But if it doesn't mess up the seals it may soften and swell them enough to slow down the leaking enough to stop the flare.
