Doing one side, front and rear drum brakes on my 71 Cuda. I mixed up the adjustment wheels when cleaning them. Which one goes on the rear, right hand thread or left hand thread?

Left/right hand threads go to different sides (not ends) of the car.

I can't tell you off the top of my head, but you can figure it out for yourself by analyzing how the adjusting lever will work the star wheel when the TOP end of the REAR shoe moves away from the fixed anchor. It is this action that should spin the star wheel so as to make the threaded assembly get LONGER.

You might want to check all four corners of the car for correct installation of the adjusters...

the adjuster cable pulls UP on the star wheel to adjust. make sure the threads cause the adjuster to grow (get longer) to push the shoes out more

Indeed, the adjuster style found on a '71 Mopar is likely to have a cable working a lever that pulls up on the star wheel.

In a general sense, it doesn't hurt to understand the concept of how self-adjusters work, no matter the make. When there is enough lining wear so that the rear shoe is drawn away from the fixed top anchor when the brakes are applied in reverse, this action pulls on linkage that ultimately spins a star wheel. On some makes, this is a lever located predominantly above the star wheel. When this style lever is pulled up, it does not engage the star wheel. The adjustment (engagement with the star wheel) happens upon return of the lever to its resting position.

Left hand thread should be on left hand (Drivers side), right hand thread on passenger side. This is the drivers side. For the adjuster to get longer, it has to have a left hand thread.