Jack,
There may be something that needs to be done, but as O gauge track is of a heavier code than OO (has this been considered, which profile/Code of rail ?) then it may be strong enough to withstand prolonged use. Also if the ends of the module track are kept within the edge of the baseboard, so the joining track rests on the module board, rather than the traditional rail-to-edge-of-board concept, it may help with the longevity.
Stu
(Main reason for this suggestion is I can't make an end plate to those sorts of tolerances.....)
Edit: Perhaps my 4" suggestion was too low, as you've mentioned 6" would allow tortoise motors.