Stuck Bottom Bracket
A 1980s Fuji should have an English bottom bracket with a left-hand threaded fixed cup.

A few methods I have used to remove very stuck bottom brackets:


Use the Stein Fixed Cup Wrench Clamp (FCC-2) to secure the wrench onto the fixed cup.  This will allow you to apply more leverage without the tool slipping off.  It also allows you to pound on the tool with a mallet which sometimes helps.
Clamp the flats of the fixed cup in a vise and turn the frame.
You mentioned keyed rings - if the fixed cup does not have flats on it, you could flatten the sides with a grinder and then stick it in the vise.
If there's any chance that thread locking compound was used (probably not likely) then applying heat would help move it.