You need to get ahold of, and speak to, one of two people at the Denver emission technical center. Either Raymond Elick or Mike Bywater. 303-744-2522
It is my opinion that they are the only people there who have a clue. I haven't spoken to Mike in a few years, but I speak to Raymond annually reguarding my diesel fleet (which has to be registered in CO). We have spoken a few times about what is required for a diesel re-power. He is a knowledgable and helpful guy. From our conversatons, the take I get from him is that there are specific things they look for in a diesel of any given model year. If your engine has the technology of a vehicle of that model year or newer, you're set. They are a state agency and I don't think they really care what the EPA has to say.
Your 90 is too short for the available diesel dynos and will have to have the idle test, which means its basically exempted from that test. They won't do much more than look at it.
I do have a 300tdi powered 110 registered here.
Full disclosure-I did it the old fashioned way. Because it was a 110 I was able to do the dyno test. It passed, and the clueless guys at the diesel test station spoke to the clueless guys at the emissions center about the engine that they did not recognize and were told that as long it was set up the way it should be on a '72 Land Rover Station Wagon
it was good to go.