I just talked to my Toyota dealer parts guy about a similar situation. He gave me a printout of the TSB covering the conversion. Toyota sells a kit of parts, but it's over $100 & doesn't include the reciever which also should be replaced.

The TSB I've got doesn't list 84, it starts at 86, so you should check with Toyota, but for 86 you need to change all the o rings, including the 4 between the compressor & the service valves. You need a new reciever/dryer, 100cc of PAG oil type "ND-oil 8" & 700g (25 oz) of R134a.

Toyota claims it is uneccessary to flush the system of old oil, but if yours has been open that long I wouldn't chance it.

http://www.ackits.com/ has the parts for far less $ than Toyota.
They also recomend a parallel flow condensor since R12 systems converted to R134a tend to be a bit weak. I'm trying to decide if it's worth the hassle since the plumbing would need to be changed a bit, but I'm leaning in that direction.

ackits has more info than you want to know about AC systems, so it's worth spending some time over there reading.

Dave