Niceguy, you're right, tighten the drive gear nut on the other side to position the shaft and lock it in place, THEN install the insert. Before you do anything though, make sure the bearing is in right, it's tapered, large side out towards the secondary so the insert will fit. Problem is if you install it backward you might not find out until you're pretty far assembled and you'll have to pull the shaft all the wway out again.
Also, the Birdman is right, when you go to the new style threaded insert and nut, you need the new washer too. It's the thick washer behind the secondary that sits right against the insert. The new insert has some pretty sharp notches that the original design doesn't have, so the washer has been changed so it won't dig in to the notches.
And try not to drive the insert in by hammering on it. You'll be banging on ball bearing surfaces and other parts. Try and use the nut to pull it in to place, the nut supposed to be tightened to 40 ft-lbs. It's a pain without Yam's special tools, post again if you need help with this part.