Their ad says these couplers will space F-units 3 scale feet apart. I tried a set on a pair of my units: they were still 5 scale feet apart! In fact, they were only a scale 3 inches closer together than were a similar set of F-units with Kadee #5s. Would be interested in knowing if anyone else has tried these couplers and what results you have had. I did not modify the locomotives in any way, just installed the couplers.
I think the ad says it spaces a certain brand of F unit to 3 scale feet.(Atlas,Athearn, I don’t remember)Did you install them on this brand loco? Other brands may need the coupler box relocated. I may be wrong but that’s what I understood from the ad I saw.
Try putting a Mc Henry # 43 coupler in a Kadee coupler box and lid. Then cut off the back of the coupler box and lid just behind the the center post. Connect coupler and box to the rear of the f unit with a screw. Do the same to the front of the B unit. I have done this with a number of my Athearn Genesis units.