73 Valiant R12 AC system pressures

I am still running R12 in my 73 Valiant with factory AC, I have a little bit less than 3 12oz cans of R12 in it now. Seems like it could get a little bit colder.

With my manifold gauges hooked up what pressures should I be aiming for? I still see some bubbles in the sight glass. I would rather go by pressure than the sight glass.