91 pa, can't get damper off

I want to replace my timing set, but can't get the damper off. I removed the main bolt using an impact driver, but can't budge the damper. I partially ground the heads of three 4" x 1/4" bolts so that I could slip them through the slots on the damper and hook them behind the damper face. Partially reintalling the main bolt and using a webfoot puller I was able to get very strong pressure pulling exactly parallel to the crankshaft. However, I did not budge the damper at all. I stopped as I was concerned about deforming the slots. I thought that possibly the main bolt had threaded into the damper, but a flashlight inspection shows the inside of the damper being smooth. Is there a key that must be removed?

Spray WD-40 inside the hub and let it sit for awhile, then put your puller rig back on and apply pressure just like you did. Hit the adjusting screw head on the puller with a hammer and tighten some more. Repeat this process until it loosens. Sometimes they can be stubborn with rust between the hub and crank. Once it starts, the worse part is over.