My '85 also only leaks after being shut off for quite awhile.  Sometimes
overnight, sometimes the next evening.  I think it is old, hard gaskets
that seal when hot, but leak when the metal around them cools and
contracts.  I also have never seen any leakage while running and do not
smell hot antifreeze while running.  The fact that it pushes it out so much
later tells me the system is holding pressure pretty well.  It is just a
matter of time until the motor gets yanked for this and other reasons.  I
do not see the levels changing or any bubbling in my overflow tank that you
say you have.  Do the bubbles stop when the engine is shut off or do they
continue for awhile? A compression leak would stop fairly soon after
shutdown?

                                                             Jay