Anyone have any info or illustrations on the best way to replace the selector cables on a Dover Composite Elevator.

yes, I've done many

Is there more than meets the eye here?

Count your wraps and get after it?

I know now rookie mistake...but in my case I sure wish I would have locked down/secured the selector drum better. Floor levels were off 5-6 inches

Be sure to use the proper cable. Selector Cable from the OEM is best.

Also spring length on bottom of car should be 20 inches, this puts proper tension and elastic stretch into selector cable so pie plates line up with floor levels . Also it might be worthwhile to check how close 0 indicator on vernier dial is to master floor before you do any fine tuning to optical leveling