I checked on this when a friend bought a car in San Francisco to take home to Vancouver.

The California DMV person I talked to said there's no permit that solely covers driving a car out of state. You don't need one if the registration is current and you have a bill of sale. The car can't be on the road PERIOD if it's not registered. There are exceptions for dealers.

If the owners put it in non-operational status, you can pay for registration which should be $60-70 for a year. Hardly makes sense on a car you're taking out of state. If they let it lapse without putting it in non-op status then any DMV transaction will include all the fees and penalties due. Again, there are exceptions for dealers and charities receiving donations.

I say hang some Oregon plates on it and drive it with a bill of sale. Or tie a string between the 81 and 83 and say you're towing it

If your 15" wheels have oval holes, they'll be a perfect fit at either 21.5mm offset (15x6.5) or 25mm offset (15x7). If they have rectangular holes, I think they'll fit without rubbing but they'll be more inboard than God intended. Those would be W124 15x6.5 wheels with 34mm offset, I think. I don't know if late 201 wheels will fit.

If CA299 is the Fort Bragg-Willits route, that road gave my AWD compact a workout. Make sure you have H4s if you do it at night.

Sixto
91 300SE
87 300SDL
83 300SD