You should be lining the films up on the pin bar that you mount somewhere on a template. Then moving the carrier sheet to the pin bar on the screen jig, which is customarily mounted to the glass of your exposure unit.
I read somewhere that some people will mouth the screen jig to a separate table (not the exposure unit) and transfer the film to the screen via two sided tape.
My main interest in this is that there is close to a $3000 difference in pries of LED exposure units for one that can do a 23x31 frame, and one that it tri-loc compatible. I would love to go LED, but would hate to lost tri-loc compatibility. Unfortunately, the price of the larger led units are out of my price range.
I also am concerned with the accuracy of transferring film via 2 sided tape.