Your high side line (liquid line) will always be the line going through the dryer returning from the evap core. The vapor line will be a fatter line that basically takes a path from the compressor to the evap core non-stop.
On the early I am not sure if this rule applies, but on the lates you have to use the suction side of the compressor, meaning that the service port is on the compressor itself. The compressor muts be swung out of the way and a charge line attached, then swung back and belted in for the charge.
I would search the archives sine I seem to remember that the early's had a low side charge port on the fender well.
One more thing, if your doing a retro consider a new condensor from
www.griffiths.com, it will allow your new 134A system to operate more efficently, and your engine will cool better.