Hello, Lyle,
I'd suggest that you will have to sacrifice one of the boards to find out how the mast track is inserted and this will also allow you to get the old mast track out. The screws that you talk about are probably secured to some sort of support, which is secured/fibreglassed into the board. As you know, screws into plastic or fibreglass would not be able to withstand sailing forces without support.
For insertion of the new mast track, you might have a look here:
boardlady.com/repairmenu.htm and read up under "Soft Decks" and "Powerbox Replacement"
As the board is in Maine, you might also post your query here:
www.iwindsurf.com/forums/viewforum.php?f=1&sid=7f9127fc640424fb452821cbef8870e1Hope this helps.