I have had this happen to me also on a 91 cherokee. It was a pain in the ***. We ended up chipping the rear of the block getting it out but just don't do that. What we did was to lossen the bearing caps really good (not take the bolts all the way out though) and this will take the stress off the top half of the seal by allowing the crank to move down a bit. Also try having a helper put a large wrench on the balancer and turning it while you get a really thin screwdriver or punch up in there to try and turn out the seal. Or use a combination of the two. Hopefully this helps.
2006 WK Overland - K&N CAI, Superchips Programmer, Dynomax Ultra Flo Muffler, 180 Degree Thermostat, 255/75r17 BF Goodrich M/T Tires, 1.25" Wheel Spacers, Resonator Delete, OME HD Lift
1998 ZJ 5.9L Limited - SOLD