Now using foil on 2009 RRD X-Fire 122L and 1990s Speed 250L race board.
I just needed to figure out how to use a 2017 foil designed for a deep Tuttle box on a 2009 board with a standard (shallow) Tuttle box that wasn't designed to take the load of a foil.
The solution* (*you can just buy a board with deep Tuttle box and get foiling) is to redistribute the load away from the standard Tuttle box and create a load-bearing 'sandwich' - to spread the load between the top (deck) and bottom of the board.
This should work for all foils with a flange - such as Starboard GT, Slingshot & Fanatic. It's a new option for people with older boards still in great condition and perfect for foiling, but limited by having a standard Tuttle box.
Note: It won't work on foils without a flange - such as Neil Pryde Alu Flight or Starboard racing foils.
This 'sandwich' method also works well with longboards with open centreboard boxes such as the 25-30 year old Speed 250L race board from the 1990s. You just need 150mm long M6 bolts.