How ("The Old Way") to install the Harmonic Balancer on a 4.3L 6 cylinder GMC Engine ?
Is their a Alternate Method.
Can you tap it lightly / continually/ surroundingly with a hammer and Large Deep Well Socket surrounding the crank and touching the Balancer ?

The last time I used the Harmonic Balancer Install and Removal Tool
( following instructions to the T ) - I had a difficult time removing the Tool's Bolt's Assy. after the install.

 

You could, you may want to use a 2x4 and a deadblow hammer. I would be concerned about damaging the crankshaft. You may try a light coat of anti sieze on the thread of the tool.

 

Small Mallet Hammer / Rubber Mallet / 2 sm. pieces of 2 X 4 / Large Large Socket.
It went on after much time hammering short blows and taking a day break in between !