O Scale decals for repaint of K lIne and Lionel Baggage and RPO Cars

COTS = Clean, Oil & Test Stencil; used to report info on car sides after about 1972, not for car lettering.  Sorry I can't be much help for other lettering sources.

Chuck

 If you can find the correct size and font. I’d give the individual letters a try.  I’d use a piece of masking tape already laid out with centering marks for each letter. Get it positioned where you want it on the car. Wabash doesn’t involve a lot of letters. Start in the middle with the B & A and work your way out. Give the first letters time to adhere well. Work your way out from the center using your marks on the tape to center the letters. Use the tape as a guide but hold the model a few feet away and trust your eyes also. Decals are pretty forgiving as far as moving them around. It’s not a one shot deal to get it right. Take your time and they should come out fine. There are plenty of threads or on line instructions as far as applying them. 
 You’ve already accomplished the hard part. Repainting the cars. If you have the confidence to do that. The decals should be in your skill level.