unfortunately, I don't. There is a grease that OME sells/includes, but despite having asked here I never found out what would be best to use. I just made a wild guess, but I hate to recommend it, since I have no idea if it's good or not. I did see that my neighbor had bought some urethane suspension bushings for a Mazda from an aftermarket place and they also came with grease. So there must be some stuff out there that is suitable. Let us know what you find, if you do look.
I would imagine calling a urethane bushing distributor or even ARB might do the trick.
FWIW, I recall reading that urethane bushings are made to rotate rather than twist as do the rubber bushings. So, the rod that the lower eye of the rear shock rides on in the 80, in particular, should probably be very clean and smooth and rustfree to prevent squeaks. I may take mine off again and clean it even more than I already did and use proper grease this time....