I've fixed the pilots on 2 MTH RS1's. I made spacers out of 1/8 aluminum. These screwed into the chassis using the same holes as the headlight bracket. I had to trim the coupler mount off the power truck for clearance. Lot's of measuring, drilling, tapping and filing. Came out okay. You said you wanted a quick fix to a Kadee. Remove the stock coil coupler. Make something along this line and secure it with a 10 32 screw using the stock couplers t mounting hole.
Still involves some fabrication but it's a one evening project. For some reason. The MTH coil couplers don't mate with Kadee's. Get a few cars up and running and you can see if this is the route you want to go. Pretty much non evasive as far as the engine in case you don't like the end result. You can go back. This is the fastest way to get up and running. If you want to go with fixed pilots you can think of how you want to go about it while your switching cars. I run MTH DL109's using these. The one pictured above is for the front of a Leagacy 0-8-0.