I think the IDO will fit on almost any board with a mast slot in it.
My guess would be the 2 bolts are in a line down the center of the board
like Deviator or Chinook 2 bolt bases.
You might look for an older Go (make sure you can find the side fins for it) or perhaps an early Start with the center fin box where you can install whatever fin you like (anything with a Tuttle head).
And, you can put a big sail on the old Start and have one of the earliest planing boards on the planet.
If your kids did not take to the Loft 3.2 m2 rig on the Bic Samba, then getting something wider is for sure your best option.
Please read over the instructional posts earlier in the thread.
If you follow them very closely, you probably do not need the IDO.
If you need further clarification, I will be glad to provide what ever I can.
Hope this helps,