Looking for info on the HIGH side ac port for r12, it seems to be bigger than the r12 low side service port?

I have lots of experience with r12 and r134a but I have never come across an r12 high side port that is larger than the low side port so I can't get my manifold to connect on the high side.

I know its not needed for recharging but helps with diagnostics


I have duracool gas to install for a r12 substitute.

 

This is a first gen dodge, seems to be in the wrong area