needing a new rear end and advice

Chrysler built a lot of 318 2 barrel a-bodeis with the 7-1/4. A stick shift would typically get you an upgrade to the 8-3/4. An automatic is easier on the driveline because there is less chance of shock loading the drivetrain. Stick shifts tend to transmit more abrupt loads. Neutral drops, burnouts, stickier rear tires would kill the 7-1/4 eventually---if not immediately.

If you want to keep the same Small Bolt Pattern you have now then the logical choice is a 65-72 a-body 8-3/4". Direct bolt-in.

Swapping a bolt-in 73-76 a-body 8-1/4 is an option but then you have the Big bolt Pattern in the rear but the SBP in the front. The 73 340 and 74 and later 360 4 speed cars used this rear.

In my opinion it depends on what you are going to do with the car and how you are going to drive it. The 7-1/4 will live for the present time if you don't abuse it.