an 84 300D with only 78K for $400.00?

I hate you already

Just kidding of course.
that is great, how did you fall into a deal like that?
anyway, welcome to the forum. start reading, listening, asking questions, do some searches, sit on the side line when things start heating up

and see where it goes. In no time you will armed to take on anything. You will be dangerious with knowledge.

.
stick with R12 for better cooling. up grading to a Parallel flow condensor will also help with better cooling.
Charlie