The BSS single trigger uses the floorplate that is configured for double triggers. You can see two blades of the single trigger going up into the floorplate.
Other designs like the Hunter One Trigger and the Parker also use a floorplate that still has the two slots for the double triggers. One slot has the single trigger and the other slot has the selector.
However, if you have a Miller or Miller copy (factory Ithaca), the floorplate will be a single wide slot. You would either have to replace the floorplate or weld a piece in to accomodate the triggers, as a minimum. There's also the issue of the sears. Look at the picture and you can see the bent sears to accomodate the single trigger mechanism. On double triggers, these would be straight.
So some guns are double trigger ready and some not.
