rout out the existing box so the fin is 47deg, and re box, chop up some old glass what ever you have laying around, add some resin what ever you have (vinyl ester, or epoxy) i used vinyl ester, till it pools , wax up board or a fine layer of plastic, dump the chopped glass on the board and lower the fin on to the chop, put some blue painters tape on one side and down too the board, get your wheel and work the glass so the resin pools and packs down, get some more blue tape and stick it on the other side, again using the wheel over the tape get the shape , wait for it to gel when its still softish trim with a blade then sand, the fin is now a useable 47deg 17