Corn head grease comes in two flavors; one for low speed gearboxes and the other for high speed gearboxes. This is according to John Deere literature, but they didn't say what they consider to be high speed or low speed. But neither one is suitable for an A transmission, in my opinion.
NO NO and again NO talk to a rep from your favorite oil company tell them what you need and they will you generally set you right [they dont want to be the cause of a fail]
Corn head grease in the steering box and around the u-joint. I cannot think of any other place in an old ford. GL4 90 on the trans and GL4 140 in rear end.
We use Corn Head grease in our center pivot gear boxes but they don't run in the winter and move at a very slow speed in the summer. You'd never be able to shift the trans. What you use for lubricant in a transmission depends on the trans.
O-ring the case in 3 places and it won't leak anymore. 1 at front of cluster shaft hole, 2 in rear inboard of lock pin-- on cluster shaft hole and reverse idler hole.