Hi ES44AC,
I have had success with 91% isopropyl alcohol & a cotton swab. I easily removed a whole road name off a Lionel Legacy Northern Pacific EM1, with little or no trace of the name. I hope to re-letter it for B&O when I have the decals printed.
First of all, I am not an expert on this & always do a test somewhere unnoticeable. You want to make sure what ever you do use, will NOT harm the body color. I believe the actual engine paints are quite durable & usually take quite an effort to remove completely. Lettering, logos & other designs are done by another process, I think its called pad printing. Possibly similar to silk screening & may even be a different type of paint.
Once you're confident you won't ruin the body color I suggest with a small amount on of alcohol on the Q-tip, carefully & slowly rub one small corner of the number. If successful proceed with the rest. You may need a final clean up with some alcohol on a cotton rag. At no point should you need to rub hard or vigorously. Lightly buff out the area with a clean cotton rag.
I usually try something like this with the thought that if I do mess it up I will need to repaint the area. You may want to see if any other members reply before you proceed.
Good Luck!
Joe