Denny,
Paper hinges with wheat paste will work just fine. I would use LOTS of hinges along the top and even a few on the sides and bottom. I don't think you will need mylar, and I don't think it would be a good idea to use it anyway on something friable like charcoal. Are the edges meant to be shown with all of their 'character' or was the piece damaged by careless handling?
Your bigger issue will be with glazing. Regular acrylic is my default glazing on something this large, but the static will be a serious problem. The only way you could use it is with a VERY deep spacer, a minimum of 3/4", I would try and go deeper- say, an inch to 1 1/2". That means a sturdy and deep frame and that means big $$$.
Truvue Optium (sp)(anti-reflective AND ANTI- STATIC) would be absolutely perfect for this piece- it only comes (I think) 41 x 71 and you could possibly make it work size wise if you got over the nosebleed price. But the extra expense in acrylic could possibly end up being less than the sturdy and deep frame with deep spacers that I mentioned above.
Make any sense?
edie mondaymentalmidget goddess