grill pops out just bring a very thin flat head or tool to avoid damaging the side of the grill.. velcro type holder and will be tight in the corners where the metal ends are
my 115 has 2 small side by side inputs in the back. you might ask them the let you pop them out and loom in with aflashlight to see the magnet....
Yep - mine too (re the grille). The first thing I do with any cab I get is to take the grille off and staple a piece of nylon webbing onto the back of the frame to use as a pull tab to get it off again in the future.... otherwise you just end up dinging up the tolex trying to pry it out (if you do that frequently , Like I do to try various speakers and generally tinker in there; the grille fit on my 115RH is particularly tight; real pain to get out, much more so than any other cab I have/had).
I don't think the jack peek idea is a good one. You'll loose the jack in the cab and won't see much if anything - I may be wrong, but IIRC, there's no jack plate to unscrew just jacks in the wood..... could be wrong though... [google, google] ah, not a plate, but one of them cups like on an old Tele - best not to mess with those IMHO). The best way to look inside the 115RH is to remove the speaker (no need to desolder, just unmount and look inside). If you just take a pic of the cone with the grille off however, we will probably, between the lot of us, be able to tell you what it is, or narrow it down considerably anyway.