This image has a SEF pack on top and an Ambi pack on the the bottom. The selector hole on the SEF pack is smaller and has a notch on top. The burst pack has a larger selector hole and another pin hole towards rear (right side of picture) of the body for some of the burst mechanism. You can watch this video for how the trigger pack works. This pdf link has good cut away drawing of the internals of the burst pack. There are smiths who have converted registered trigger boxes from SEF to Ambi, but your pictures look like it's still a SEF box.