Thinking about selling..need advice

you can add AC with a Vintage Air or Classic Air Kit, and as stated a Gear Vendors OD unit, or if you don’t have the inclination to do the install yourself have a reliable shop do the install and have what you want.
Depending upon where you live, the AC and OD parts would be a wash with newer car plates and newer car insurance and newer car depreciation in a couple of years.
Agree 100% A/c is a nice creature comfort option for sure and depending on your car, usually ads value down the road. O/D would be great as well. Something I thought about while driving 4 hours north to St Paul earlier this year. A friend found a lock-up 904 for his Barracuda. I bet that lock-up ads a mile or two per gallon. A overdrive, even more.