Do you mean retro rail instead of classic RT rail? A classic RT rail only works with Classic RT valves and bodies and has the air passages that feed the valve through the banjo bolt at the rear of the rail. Classic RT bodies, rails, and valves have different dimensions than others that AGD sold. An X valve will not even install onto a classic RT rail because the X-valve has a larger diameter than a classic RT valve.
The RT Pro sear is designed to work in the retro rail. The back of the sear should fit up through the hole in the ULE body.
Except for the Automag in front, its usually the man behind the equipment that counts.