I've been using this width ( 27") since 2002, you'll see it on many of my boards including the 'Makaha' 12-9 shown on the earlier thread.
The panels shown will be trimmed about an inch on each side so are wider than the finished board. Thickness is only 2.5" so the board isn't for standup paddling.
The 'Thumb' looks very nice indeed,and this sort of shape can take all sorts of fin setups. Due to the long converging rail minimal or no toe in is needed on side fins, although it can be used.
The only shop I know selling them recommends you ride them a couple of inches shorther than your HPSB. I'm thinking 5'10" x 21" x 2 5/8". So yeah, definitely not quite 10'6" x 27" x N. They're real short and maneuvarable, but apparently have great hold due to the pin tail. As a single fin, they just want to go straight, but the bonzer setup is apparently where it's at. They're actually an old design from 70's that just recently started making a comeback in SoCal.