There are several books that cover the subject of lofting. Simply put, the numbers relate to specific points on the hull at each station. The heights are (in this case) measured up from the bottom of the lowest point on the keel (as noted in the offsets), which appears to be straight from station 5 aft.
The half breadths are measured away from the centerline of the boat at the sheer, upper and lower chine and the keel (again as noted in the offsets table). Also noted in the table is all measurements are to the inside of the planking, which is a handy feature when making station molds.
This boat isn't designed to be over powered so keep the HP modest. The numbers used are displayed in feet then inches, then eighths of an inch. In other words the notation 2-3-4 actually means 2' 3" and 4/8" (1/2"). Most modern designers have stopped using these old school dimensioning on offset tables, preferring directly read dimensions such as 27.5" for the same offset as I previously mentioned, but some still use the old method. I have to admit some of my older designs have yet to be converted.