I have always used a socket that just barely fits into the cases. I tap the shaft in gently until it is seated then once seated use the socket to drive the seal in. IF you heat the cases a little and put the shaft into the freezer it will almost drop in by hand.
I have done many this way and never used the "pusher".
Look in my 96xp or 98 spx resto thread. I use a 15/16 deep craftsman socket and show pics.
More importantly........did you look at the drive gear on the crank? Is it centered? If not you'll eat the new gear alive. Not sure if it had room to move on the smaller cc engines but they would slide on the 717 engines. And eat it up.