Alrighty, no shark talks here! I have a short board (6 x 18 or 19 (can't remember) x 2.25) that's just sitting around doing nothing. Was super cheap so don't mind giving it the chops.
I want to try converting it into a single fin (remove the centre plugs and insert a fin box). Honestly not too worried about the end result but will be stoked if it works. Anybody with tips/ tried this before? Will probably end up screwing up and leaving it to a shaper to pick up the pieces 
G'day - ask in the LB thread - someone did it recently to a tri-fin mal... thread had pics and some discussion on the fin placement (even cut the back section out of a regular fin to get the right placement).
Mac or Lacey will know who's thread it was...
This is what your looking for, because the rear fin on a thruster is back further than you ever need to run the single fin you can leave the fcs plugs in the board if you cut the back out of the fin, makes the job a lot easier than taking the plug out,this set up works really well on this board, I am loving it as a single fin.
I done a couple like this that worked....
Can u get hold of a router?, grab some plywood sit the box on it mark round the box (couple of mill bigger) to make a template.
Put fin in fin box.
Once you've set up and routed it out pour a bit of resin in and sit the box in with the fin.
Set the toe and cant using the fin with tape.
Let set and finish off.
