Sometime in the '80s a dealer I worked for bought a nice '73 wagon. It had a miss in it and I bought it for something like $450. I suspected a bad spark plug and sure enough the 400 had 7 new plugs in it and one that looked like it was original. IIRC the 8th one was kind of hard to got to so it was never changed. I put an new one it and and that 400 ran much better than it should to be in a big wagon.