It gets better with the Intermountain. On one car, I pried open the coupler pocket, pulled out the Kadee #5 and installed a pair of #158 I had, that had already been painted boxcar red. Crude, but an easy fix. The couplers still operate.
Yesterday I tackled a pair of UP cars. I had some Kadee #158 with the #262 scale width coupler pockets, and a couple pair of more accurate trucks (Accurail "Bettendorf" with code 88 wheels) and painted them oxide red. So today I pried off the entire Intermountain coupler box, which was easier than prying it open. Then I went to tap the existing holes. because they were in the right place to mount the coupler box in the right location. Wrooonnngggg -- turns out the RTR Intermountain cars have a steel weight firmly glued to the inside of the car floor, and the weight evidently extends from end to end. I didn't disassemble the car to determine this, I just discovered that my tap won't go into the hole because of the steel weight blocking its path. And the magnet test confirmed the weight is steel. So I won't be drilling through it, not with hand drills in pin vice (vises?) Sorry Tony, the plural of vise has to be something like "vice".
I would prefer to use a screw to hold the coupler box onto the car, but I'm thinking of using a brass rod of about the right size, cutting it to length (bottoming out in the hole and extending through the hole in the Kadee box, and using Shoe Goo or similar to attach the rod into the hole and the coupler box, which would at least sustain the draft forces of normal operation of these cars in a train.
Another thing I thought of is chiseling the roof off of these cars, removing the weight and installing a more typical weight in place of that steel weight, which would then allow me to thread that hole and attach the coupler box in a more secure manner. Needless to say, this thought makes me a little queasy, but I've whacked the roof off an Intermountain pair of reefers before when it turned out that the wrong one was installed on each car.
Or I could put these cars in the driveway and run over them a few times, which is probably the most appropriate thing to do with them, since I have four more that need a similar treatment.
Seriously, any other suggestions? Suggestions that don't involve leaving the installed, unpainted, #5 alone?