rBrunckhorst
Charging the system is nat at all a difficult proceedure, but in your case the system is probably not marked as to how much refrigerant to use (most production vehicles are clearly marked. This is really only a guideline anyway. I would suggest that you make sure that your receiver/dryer is new, make sure the expansion orifice is clear, or just put a new one in, and vacuum the system for about 1/2 hour to boil off any moisture that is in there.
You can figure out the charge a couple of ways. One is a sight glass which you may not have.Or look at a chart for a current production vehicle and measure under hood ambient temperature and charge until your high side reads to the corresponding pressure (approximate), or most tool manufacturers have a clamp on tool that goes on the metal lines and sonically looks for air bubbles.
All of these methods work well, depending on the system, but I have found that common sense goes a long way and if you are charging the system and it suddenly gets warmer you may have too much refrigerant....time to bleed off a little.
The bottom line is put in the correct oil, if the system cools well after charging, you are probably in the ball park.
Just be careful with hoses and connections as there are some very high pressures to deal with.
Good Luck
Phil