Ed,
Unfortunately, the answer you get at the Reno DMV is going to depend on WHO you talk with down there. They LOVE the power they have and like to assert it wherever they can.
That being said.... My rig (being a 76) fell under a different emissions era, so it made my life much easier. Mine did not have to be OBD compliant and I was held to the 76 emissions standards.
Now I do know that after 80 year, something vehicles,, the rules completely changed and one would be required to have full OBD II Compliance and emissions and the engine needed to be the vehicles model year or newer.
Mine is a gasser too, so I can not speak to diesels at all.
I checked w/ them through EVERY STEP of my build, every few mos. just to make sure the regs hadn't changed. Everytime I went there, I'd get a different answer (one that was NOT good news for me) and I would make them refer to the supervisor to get the final word. At that point when I got the REAL story, I would grab a biz card of whomever I was talking with, write down the date and time and a brief statement of the topic discussed (so I could recall it) and stick it in my wallet and HOLD ON TO IT!!
When I did go in for the final check off, the SUPERVISOR tried to EFF W/ me!! He said "well, you have the OBD and emissions connected?" I said, "well, per YOU, its not required." He said "who told you that?" I then Whipped out my cards and the dates and times and started rolling them off... He then said "okay, well go ahead and write it up." The point I'm trying to relate... COVER YOUR ASS! They can be real PRICKS!! Also, even IF the first guy you talk to says "yeah... That shouldn't be a problem. " DON'T BELIEVE IT!! Make the KNOW wether its NOT or IS a problem.
They could give a F@CK how much you've spent or how hard you worked based on BAD information THEY have to you, so its up to YOU to make them commit to what they tell you. Also, the regs do seem to change FREQUENTLY, so keep checking back.
HTH!!
K