I'm assuming since the manual suggests only a single, 45oz-in servo for both elevator halves, two servos with 30oz-in each should be enough...?

The HS82MG would be cool just because the size is good and the weight is good; just over a half-ounce each would probably be perfect for my balance issues. I am not thrilled with the way this plane flies so I want to add as little weight as possible, and the HS82's would actually not be adding weight, just moving it back. The battery is strapped to the rearmost former in the (cabin?) and there is lead on the tail, so plenty of room to shift weight forward if need be, when the job is done.

So my plan is to cutout two servo mounts from ply/hardwood - a solid piece with the servo hole cut from the center, and glue it to the balsa sheeting. Should I bother with trying to taper the servo mount? Probably more effort than it's worth if I'm going to use ball links.

I have two 1 3/4" titanium rods to use. If I stagger the servos so one is just on top of the other (but on opposite side) the ends of the servo arms should pretty much line up perfectly. This would put the arms positioned with one on top and one on the bottom (however I have a SICK new radio so that part doesn't really matter).