Brake Tee on Rear Axle and Hardware?

Folks:

Someone screwed up the mounting of the brass "gold" tee on the rear axle of my 1968 Dodge Dart SL-6/225 ci. Here are my questions:

(a) what size bolt in diameter, length, and screw pitch goes through the tee and screws into the rear axle (0EM from the factory)?
(b) should there be a vent as part of the bolt system?
(c) why do we need a vent?
(d) is their an assy that contains the bolt and vent??

Long story........but it looks like someone tapped the hole to 7/16 in diameter to match tee hole diameter and I removed a partially screwed in 3/8 in bolt to secure the tee. The tee is bouncing and flopping around and is a real hack so will fix it right. The threads are screwed up also in the axle.

Thx....a stupid problem as you can see........MOPAR Gods please help.

Love MOPAR...Love my DART.....Thx and appreciate the help.