My A.C. Compressor on my '79 300 SD just seized and threw the belt. Can I still drive the car until I repair it?

I see I have the R-4 compressor. It is around 275.00. I will have a tech who filled my system before replace it.

Would it be a good idea if it is possible to upgrade the system to the current refrigerant? If it is possible, what all would I need to replace?

[Edited by patsy on 12-05-2000 at 08:50 PM]