<<Good morning John!! Any idea what the 3867 code is for?? >>
Back in '55-'56, engines carried sequential serial numbers (unrelated to car serial numbers), normally stamped on the front pad, followed by the code for the plant, date, and suffix (photo of '56 pad below); that might be what the 3867 is, although it's covered by the front of the intake manifold. That's a strange one.