Just to conclude --
Took out the replacement used tranny, opened the top, played with it a bit, but still
couldn't get it to shift into 1st and reverse while on the ground.
Ended up putting back the old transmission. It works as before. Not ideal, but this is my
daily driver so I'll make do till I find a 'good' replacement. The one I got was obviously in
a pretty bad shape.
So, in the end, all I got out of the whole exercise: a new seat and socket. a 12 min replacement. LOL.