3 footed towers were "standard" towers intended to be topped with a radar, such as the one which still stands atop Mont Ste-Marie.
|Lac Ste Marie Gap Filler Radar- 2012|
4 footed towers were to be topped by a radar, but would also have a fire tower / lookout directly underneath, such as the one at Timmins.
|Timmins Gap Filler Radar Station - August 2013|
Here is a list of all the Gap FIller Stations which were partially built, and the kind of tower they were intended to have (Documented by DND on Feb 13th 1963). This is not an indication that the tower still stands there today, or was ever erected to begin with.
|Algonquin Park||Standard Tower|
|Elliot Lake||Joint Tower|
|Lac St Marie||Standard Tower|
|La Tuque||Standard Tower|
|Scotch Settlement||Standard Tower|
|St Josephs||Standard Tower|
|Summerville Centre||Standard Tower|
|Todd Mountain||Joint Tower|
In the end the program was cut due to budget cuts, and by 1964 the land and partially built structures and buildings were being sold to private interests.