RWTD

I have the original chain on a mid 80's Fuji Royale sport tourer with the marking NKK on each outer plate.I was repairing some stiff links with a chain tool and noticed an outer plate and one link over an inner plate were bent causing the stiff links and unable to be bent back.So I removed the pins from the outer plate planning to replace it with a spare outer plate that came with the tool however try as I may I cannot get the pins back into the spare and even broke the tool trying to force it .There was a second spare outer plate with extra long pins with grooves that a fastener attaches to that I was able to hook up but this won't make it past the rear derailler mechanism.The questions are what am I doing wrong in replacing the outer plate,is it possible to still replace it and could I just get a new chain without replacing the rear gears which are the originals and if so would a standard multispeed chain do.