How to remove old style chainring held in by a single nut between bearing and chainring? I've got this old school mountain bike, back from 1986.  It's a 5 speed rear cassette with single front chainring.  Make unknown, but has an emblem on the front that says "Concord".  I'm jammed up trying to get the chainring off.  The chainring removal requires removing the crankset as the chainring will need to be slid all the way off the "left" side of the crankset.  It's held in to place with a single large nut around the crank (which the Park Tool HCW-18 3 pointed side is a perfect fit).  To keep the chainring from slipping under power, there's a pin from the right side of the crankset that pokes into a hole on the chainring.  So, relatively straightforward:

Except, the big nut that holds it in place is giving me fits.  It's so tight I can't even figure out if it's right or left threaded!  Since it's on the right hand side of the frame and bearings I figured it would be right hand thread.  However, since it's facing from the frame/bearing side out away (with the chainring out further from the frame), perhaps it's left threaded?

Won't budge with muscle power.  I've also tried tapping the HCW-18 with a rubber mallet in both directions after using PB Blaster on the nut.  No go.  Can't seem to get any motion at all in either direction.  I'm about ready to go at it with my 20lb sledge to either break it free or just plain break it, but would like to have some idea which direction to go first...
No exposed threads to check.  The Sheldon Brown site was helpful in general, but couldn't answer the direction, but led me to find a Park Tool page which suggested it should be right handed.  That knowledge combined with the PB Blaster sitting on it for a couple hours and I was able to break it free with a few hard hits from my rubber mallet again.