
You COULD do #1...but I wouldn't because it would also require a Form 337 as a major repair.
I don't think you can force Avion to do something like obtain an STC. It's not THEIR fault you purchased an airplane with documentation that's less than perfect. (And although they offer their product for use on an airplane, since it's an unapproved part, with no PMA, and no STC, then installing it becomes the responsibility of the installer...and I'll bet their sales literature also makes reference to that fact.)
The third option is probably your best one. Since the airplane has been flying with that panel for so long, it's likely that your IA whom has been signing off your annuals will feel somewhat interested in getting the FAA/FSDO inspector he works with to approve the panel. A Form 337 showing approval in block 3 of another 170 with the Avion panel would be a big help.
Does your Avion panel drastically differ from the original? (For example, does it center-stack the radios?) Or is it merely a new panel with relocated instruments? Two folks that may be helpful to you are Harry Dellicker of Del Air in Porterville, CA, and Johnny Williams of Ducote, Tx. Both can be found via Google or the TIC170A directory. Both of them have experience in getting new instrument panels field approved. Keep us posted.
I sounds as if your panel was signed off as a minor repair (...in accordance with... language.) Your own IA is responsible for accepting that description as appropriate when he approved your airplane for return to service following an annual inspection. I suggest you include him in your deliberations. He may simply advise you to leave things as they are.