He is talking about the King Pin on another style of tractor. We don't have them.
I have the 4500Z and can, with quite a bit of trouble, grease from either side with flex hose. I do cheat a little and loosen the grip of the zerk coupler just a quarter turn or so. If you do that, take extra care to hold the coupler very straight onto the zerk. I thought it to be almost impossible to grease it from the right side as Ventrac instructs, but after their video I took the challenge and succeeded. Still easier from the left.
prs