I'm looking to put a UL frame from a proto pmr on a super thin custom rail

How far down from the top edge (where the body sits) to the RT sear pin?

is the sear needed, can I just trip the on/off with a pneumatic piston?

What is the front of the sear for? not the "bolt hook", the nose

What would be the easiest way to make the concave rail top using a drill press?