Dave

The Martin OM are small bodied (same size as their 000's) but Peter Bartons' site doesn't give any dimensions so I don't know exactly how his OM compares. FYI the Martin 000/OM dimensions are:

Total length      39 13/16 inches
Body length       19 3/8
Body width (max) 15 3/16
Body depth (max)   4 1/8

The scale length of the 000 is 24.9 and for the OM, 25.4 inches (i.e. the 000 is sligthly easier to play, but less able to take low tunings.)

Pete