Some little Chevy sedans, Monza I think (not the Corvair Monza)also had to have the engine at least loosened on the mounts to get the back spark plugs. That car was designed for a rotary engine, then fitted with a piston engine when G.M. abandoned plans to use a rotary. When the word got out about the sparkplug situation, someone from the media got a chance to ask a G.M. exec how they explained something like that. He said, "we call that a design variation".