I also am trying duracool in my F250 diesel. Seems to work okay up to this date. I know from my research into the product that it is a cocktail, mostly comprised of propane (if memory serves, about 38%). When I looked at its thermal properties, it seemed to follow the R12 curves fairly closely, however, if you have leakage, the first thing to leave will be the lower volitiles leaving a mixture that the distributor up here would not tell me what it was.
For your situation, I would use the original R12 lubricants (don't know the quantities). Thats what the compresor and seals are expecting. The actual duracool doesn't care what lubricant is used so its only the original manufactures hardware that may be effected.
Good luck with the experiment. (PS I agree with your point, your running a very combustable fuel....gas. Should you develop a small leak, it should disperse readily. A guillitoned line however may be more hazardous).