Did you make that jig?
Yes. I've made many platens (before I realized too much flash heat was warping them) out of MDF (home depot) and skin top and bottom with Formica (contact cement for glue). The only other thing needed is wife's rolling pin to press out the air bubbles and a router with a ball bearing trim blade to trim the edges.
I made the registration platen to be just about 1/2 inch narrower than the Newmans so the right side tube can bump against the stop without falling off the platen.
I printed a blank film master with every registration possible and taped it to the platen. All art matches to one of the vertical, horizontal, or pocket registrations making it easy to line up on the master. I barely tape just 2 edges of art films down and use double sided tape on top to press down on the screen to catch the film and lift so everything stays in right spot.
Like I said, the real bonus was being able to slide the exposed screens back into each head using the same 3 points to pre-register the screens to print. Rarely have to make much of an adjustment.
PM me if you want more info.