Is there something written about how to convert from horn hook couplers to Kadees?
Check the Kadee web site, www.kadee.com. It’s not a universal step-by-step manual, but for most upgrades all you have to do is unscrew the plate holding in the old coupler, take that one out, put in a Kadee with its spring, and put the plate back on. After that, it’s highly adviseable to get a Kadee coupler gauge for a few dollars and adjust the coupler height. You might also want the Kadee trip-pin pliers to help with the adjustment.
Of course, if you’ve got really old equipment like I do, then every replacement is one of those “engineering challenges” that make model railroading so much fun.
Replacing any coupler, even the non-Kadee knuckle couplers that come with new equipment, with the appropriate Kadee is the right thing to do. Accept no substitutes.
Welcome to the forum. I found good dirrections with the Kaydee packages. Each application will be different and some are tricky. In almost all cases what you need is in a standard package. For the unusual ones, you have to deal with them individually.