I have been using my OD with 12 volts negative ground for about 2000 miles now. Ross Miller provided the OD and solenoid in my car that has been working flawlessly for 2 years now. I don't know what he put together, but he may also be able to help you. (When I asked him about this combination, he said he would have to get creative -but it works) After having an OD transmission, I wouldn't want to go back to life without one!
The R11 OD used in your car did have the convenience of 12v solenoids being available since their use spanned the voltage changeover years. The basic R11 electrics and mechanicals were used in many other brand cars so making repro solenoids was also feasible.
Unfortunately for the R9s as Packard used from 40-48, the overall electrics are more complicated so the solenoid is completely different electrically. The solenoids have 4 terminals and the two coils are brought out separately and powered differently as well as contain a switch to turn off an indicator light. Mechanically they are not interchangeable because of different stem lengths. Because so few cars in the overall production had OD in those years, I doubt the market is there for any R9 reproductions where it would be a simple matter to put in a different voltage coil for the limited conversion market but doing that would lead to other issues.
It might be possible to swap guts from the two solenoid types to make a long stem R9 12v solenoid that would mechanically fit but that would take some doing since the coil portion is crimped into the case. Because of the way the coils are powered it would also take a new pair of 12v relays which would also need to be reproduced and because one relay coil is in series with the solenoid hold coil it would need to be a properly calculated relay. Simpler would be a partial conversion to R11 electrics and a 2 terminal long stem solenoid and single relay but now you are into the authenticity look in giving up some R9 functions but needing to keep others because of the mechanical differences between the two units. The thought, time and $$ to make it all work would lead to a headache -- or drink.
The annoying part is that according to the parts book there was 12v export electrics for 40 models but apparently those were so rare as to have long gone extinct.
