This 1931 Martin OM-18P represents an extremely rare case, wherein "original" is not better as it relates to a pre-war Martin.
The OM-18P was produced in small numbers in 1930 & 1931, before being discontinued (evidence of its scant popularity). To be fair, the OM itself was still new, having debuted in late 1929; and a plectrum variant, hence the "P" in the model nomenclature, must have been seen as somewhat limited. Players used to a four-string neck, and in need of the bright, snappy sound associated with it would likely have already been at home on either a tenor guitar or a plectrum banjo. And guitarists intrigued by the new 14-fret OM would likely not have much use for one lacking the low end and broader dynamic range provided by six strings. In today's modern acoustic landscape, a plectrum guitar with an OM-sized body is an interesting concept for mandolin players who use their instrument to accompany their voice ...
But still. Who among us would look at an all-original 1931 Martin OM-18 with a four-string neck and not think, "If only it had six strings!" And if we could wave a magic wand and have said guitar converted to six-string setup by anyone in the world, who would we choose? We know who we'd call first. This guitar (serial number 46808) has been converted to conventional six-string setup by TJ Thompson, who made the neck and bridge seen in our photos. The original body of 46808 remains in excellent vintage condition: structurally solid as a rock, crack-free, with just the right amount of wear (someone certainly liked to strum around the fingerboard extension). This is a great-sounding guitar, with a mature, woody voice, and the expected clarity and response of a 1930's Martin OM.