R12 ain't cheap - Help me avoid $$$ mistake.

[ssuesens]

I have been tinkering with my factory AC since I bought the truck last fall. I believe I am ready to pull a vacuum and recharge the system with R12 and mineral oil. As you know - R12 is EXPENSIVE and I don't want to make a costly mistake.

Here is my progress to date:
Disassembled and cleaned all in-cab components (vent, heater core area, etc)
Replaced all vacuum lines and verified all are functioning as designed
Verified compressor is kicking on when switched on in Cab
Replaced leaking condenser (pinhole) with used unit - (pressure tested and flushed)
Replaced Dryer/accumulator
Replaced Schrader valves and o-rings
Charged system with 150# Nitrogen to verify no leaks- pressure has held for 7 days
Paid way too much for 12 cans of R12 (USA) Freon

I think my next steps is to pull a vacuum for one hour as a final leak check. If it maintains vacuum, I will then add 3.25 LBS R12 (per assembly manual) and some quantity of mineral oil. Manual says 10oz but how much is in there now?

Before I start tapping cans of this liquid gold R12, are there any other steps or final checks I should make?