Are you "collecting" these as collector items, or are you just accumulating them to make a model train set to run and have fun with? I ask because swapping the couplers from the original horn hook to Kadee would ruin any collector's value they might have.
Second question is if the Bachmann locomotives were purchased new or 2nd hand? The photo really looks like Kadees were added by the prior owner. Most new Bachmann equipment would come with McHenry couplers. McHenry's are also knuckle couplers and look similar but are made of plastic. I ask because if a prior owner performed a conversion, then they have modified the factory mounting and used a Kadee #37 undershank coupler. It would be hard to go back to the horn hooks. Here is the official conversion from the Kadee site -
https://kadee.com/conv/pdf/b10.pdf
EDIT P.S.
You know, ... now that I went back and stared at that conversion diagram again, it might not be all that hard to convert back. All they have really done (if this is indeed what they did) is to file off the built in coupler box and mounting pin. The new screw replaces the mounting pin. One could replace the copuler box with a Kadee standard and mount the horn hook with a washer (to keep it centered on the screw). I could send you the horn couplers and a couple boxes if you would like to try to convert it back.