Soak it down with some penetrating oil..You can use thread cutting oil, acetone mixed with some transmission fluid, liquid wrench, whatever..
If you have a crank bolt and a hardened washer, run it down tight before trying to remove it (it is easier to pull it on further than to pull it off).
Then when you are ready to remove it after a few hours, grease up the pointed end of the puller, remove the bolt and washer and apply slow constant pressure with a quality harmonic balancer puller, preferably not a Chinese POS made out of rings from a Cracker Jack box...
If it does not begin to move with over 80-90 ft pounds of torque on it, try using a dead blow hard faced hammer on the end of the puller jacking screw, but put some safety glasses on... Don't hit it too hard and be sure to hit it straight so you don't jack up the head...
If you heat it up, you will virtually destroy the rubber isolator (which sounds like you already knew).
I have seen some pretty stuck, but so far never had to burn one off...did a small block years ago that pulled the threads right out of the balancer, so now I use a jamb not on the bolts...
Another little tidbit...Be sure the puller is perfectly straight. If even slightly offset, much of your pulling power will be reduced because of the angular load.
Good hunting.
GT
