I can't comment too much on the FAA opinions. I'm not an I/A, and live in another country.
My understanding was that the FAA was accepting the Dynon as a backup instrument only, and typically a backup to an EFIS. If the type certificate for your airplane requires specific flight instruments, then those instruments need to be PMA'd and TSO'd. If they are not listed, then they were optional, and you could probably replace them with a non TSO item such as the Dynon, as long as it's considered a minor modification. An EFIS typically needs backup with a turn coordinator, airspeed, and altitude instruments. The Dynon EFIS really becomes nothing more than an unnecessary accessory in the eyes of the FAA. As long as it's not going to have a negative impact on the airworthiness, the FAA doesn't care. No electrical or fire risk-no foul.
The type certificate refers to the CARs in effect at the date of manufacture. If you have the original equipment list it may list the instruments that were standard, and those that were supplied as optional. If you don't have it, that's where a forum like this may turn up someone who does, or who knows. You'll see on the TCDS, that the airplane is to be placarded for Day-Night-VFR-IFR as applicable. This would have depended on the flight instruments, lighting, and avionics installed at time of manufacture. Note that if you sorted all this out, and stripped your airplane out to be Day-VFR equipped only, no amount of instrumentation from the non TSO world would get you back to Night-IFR.
A new DG and AI aren't horribly priced in comparison to the rest of what you're proposing to spend. I highly recommend you just bite the bullet and change them both as part of your upgrade.
Background. Our flying club lost a young member 10 years ago in a Cherokee 235 that was still equipped with the early black and white AI, and the hockey puck DG. He lost it in a turn at low altitude trying to retreat from some bad weather after dark. Bad decision making to end up there in the first place, but I'd had trouble interpreting those instruments after transitioning from a newer Cessna at a flight school. I've never blamed myself and the other members, but often, and still, wonder if more modern gauges with a more intuitive user interface could have saved his life. Remember the Buddy Holley story with the non standard Sperry Gyro?
If you've flown this airplane for years and years, and are intimate with the old gyros, then please disregard.








