Affordable gantry shift workholding

Hey all, I am looking for options and ideas to make a gantry shift clamping setup but I am limited in several ways on space. I need it to be as compact and perpendicular as possible and still have 6 inches of space to clamp. Ideally it would work with just about anything 6" x (up to table height) x 48"

My current table setup is a Rockler rock steady table 56"x56" with a 5’x5’ Baltic birch top.

I made a really simple setup:

Basically all you need is something secured to the table top, and a way to clamp — I was using a board and a pair of clamps hooked into the front plates (this was on an SO3).

That said, what sort of work do you need this for?

If for joinery, why not just do blind miter hidden box joints which can be cut flat on the machine?