Legally you're supposed to have someone to evacuate the system. R12 is nasty shit, eats up the ozone layer... that's why they went to R134a.

Once the system is empty it's easy enough to change out all the parts. If it was me I would change out the dryer and the compressor and just blow compressed air through all the lines. I believe the expansion valve is under the dash (never had to replace one of those on my 240's), but the rest of the components are in the engine bay and easily accessible with the motor still in the car. You don't need any fancy tools except to recharge the system, but again, I'd take it to an A/C shop to vacuum the system down and recharge it. I've recharged the system without vacuuming it first, and it worked OK, but I feel like it doesn't work as well that way.