The shifter "snout", as shown in the pirate picture, is not explained in detail.
Drive the roll pin out of the snout, and drop the piece that engages the shift rail. Either you will see two square cut rubber-ish o-rings(? not o-rings, square like some seals) you will see pieces of said, or you will see two bare grooves.
Whatever GM used hardens up and falls out. I had no luck finding any o-rings that were large enough diameter, with a thick enough ring, to make the fit tight. Some have as I recall, I didn't have many to choose from. I'm sure the GM ones were much tighter than what I ended up with. In any case, I found some o-rings that were better than nothing, and installed them.
There is a huge difference between my 1986 tranny and the 1974 tranny it replaced in the way the shifter feels, and it is definitely not JUST the o-ring, as I didn't really fix the problem with the shifter itself. Probably just general wear and age. For one thing, I guarantee the shift fork coatings are mostly/all gone in the '74, and in much better shape on the '86.