Hmm.. Looking that over the attachment point for the servo (I'm assuming it's up top) would put quite a strain on it.
If you put the connection point about half way down the short red arm, (in Fox w 's diagram) would reduce some strain, but would require a greater travel (gearing?). Though possibly increase slop.
Personally, for action on both areas, facemask and Chin, I'd be more apt to try a 2 servo hookup, one for raising and one for open the chin area, could be simultaneously activated by Ying the harnesses together and depending on gearing and servo wheel/arm choice, be more independently finetuned..
Just my 2 cents..