Hope it really is better late than never...

When I re-installed the AC in my old Galant (2.0L turbo), I remember roughly eyeballing it. If you're sure you've got the right oil for the refrigerant you will be running, it should only take something like 2-5 ounces. I found this chart, which shows Montero, but does not differentiate by engine. You have to scroll down a bit, but it looks like most Mitsubishis take about that much.

The amount of oil you use will be dependent on whether or not you drained the old system. Much of the oil lives in the compressor as far as I know. If you didn't remove it, you probably have most of the oil you really need.

Make sure you oil up the new o-rings you got for those connections in the stuff too.

I'm sure being absolutely accurate matters, but I was planning on running one of those propane kits from Amazon and ended up getting an R134 charge from a pro shop since they pressurized the lines instead of drawing a vacuum like I had planned. Car blew 45*F at idle in 110*F+ ambient here in Phoenix.

Currently do not have AC in the Pajero. It's black. It was 114*F outside for my hour long drive home yesterday. Really hope this info helps you out, brother.

Brian in Arizona.