I recently put an Edelbock 4 barrel on a 283. I can be set up by connecting to the vacuum advance to eith "timed" or "full vacuum". I can't tell which to use. When hooked up to full vac, removing the vacuum advance line effects the timing. Then attached to timed port, it seems to hve little or no effect. Which do I use. Then how to I adjust the timing correctly for that port. ?

The old 283's all used manifold vacuum for the vacuum advance unit on the distributor. That would be my recommendation. You disconnect the vacuum line at the distributor and plug the line. Then you set your initial timing to spec and finish by reconnecting the vacuum advance line.