Pickups didnt get a 312 engine and I thought that was the only vehicle that used the underhood crossover pipe.

Oldmics

I can't think of any crossover equipped 312s.  '56 passenger cars had crossovers, but only with the 272.  '54 and '55 passenger also used crossovers, but obviously did not have 312s.  Oh, just had a thought.  How about industrial applications, like chippers, lift trucks, generators, pumps, etc?