It's not too hard if you have the right equipment. A GOOD vacuum pump (Dayton, etc, not some lame-ass Harbor Freight model) a good set of manifold gauges and a huge dose of common sense. Buy new hoses or get yours rebuilt, a new accumulator, etc. It won't be cheap. It's a waste of time replacing o rings on 20+ year old hoses. I am going to do the R134 conversion, I only have 3 cans of 12 left, and the Cadillac needs them more (daily driver) than the TR. You need to make sure you use the right type and amount of oil for the refrigerant you are using.
If you know Jim Testa, he can offer great advice too.