Is this still the Baker/Hill transmission sun gear? If that's the case, the only way I've found that works well is to suspend the shaft vertically by supporting under the inside disc and drive the shaft down through it using a brass or aluminum punch. Make sure you place a rubber or wooden block under the transmission shaft so it's not damaged when it falls.
Stuck in the seventies- not in the swamp.
(6) Attex, a Hustler, a Super Swamp Fox, (2) Tricarts, (3) Tri-sports, a Sno-co trike, 3 Dunecycles, and a Starcraft! ...so far