Specifically the central gutter. Is there info on the miter like box construction from extant samples, front facing plank over the 2 perpendicular planks or the front facing plank between the 2 perpendicular planks ?

My guess would be the first since that would seem to be more resistant to impacts from the front.

I'm not going too historical for the first try, ie, no hide glue, traditional gesso, lime wood or beech. Just plain old PVAc (white) glue, fir etc.But it will be made of planks only, no plywood.

I don't have an adze so hollowing out a big beam wouldn't be ideal.

Good question...

I made mine (also planked, but with largely modern materials) with the facing plank over the two perpendicular planks. Seems more logical.

I just found this http://www.bettinaschreier.com/equipment/e_pavise.html and there's a link to a thread here on myArmoury.