Would the following info help you?
(Excerpts from a previous thread).


Width (or height) is just a bit shy of 8.9cm, (maybe 88.5mm to 88.7mm).
Start wide...then draw-file or block-sand for a perfect fit.

Length is at least 14.3cm.
You could run this measurement longer, for a handle/grip...if you want.
I would...by about a 1/2 inch.

Thickness is no more then average matchbook cardboard.
(Sorry, I don't have my calipers handy).
OH--it is EXACTLY the size of a 3x4 graflex film pack back--I needed one and had one of them laying around..tried it PERFECT FIT--and a good use for the pack back

longer is much better though--you're better off making one that has a little extra length to grip---or just add tape for a pull tab