When I took my distributor out in 1996 it had not been loosened since aprox. 1973 and had over 120,000 miles in that position. It took an acetylene torch to get it loose. Recently we also recently used a tool called "Bolt Buster" ( an induction heater) to loosen nuts, bolts, distributors, engine block sending units and fasteners We were able to free up a frozen top frame on a 1965 Galaxie that had been sitting outside for 9 years uncovered. It took a lot of PB Blaster, Kroll and even WD40, but the heat seemed to get it loose the best. Be careful prying on the distributor as they tend to break at just above the manifold level if the pressure is too great and with the aluminum construction its easy to apply too much pressure.
They are also right about the O Ring, it gets rock hard and seizes to the block, extremely had to break loose and even then its doesn't move well.
This is an item you need to take you time with to avoid damaging or destroying the distributor. The strap wrench idea seems to be the best for attempting to move it
Good Luck