I think the railroad has some stencils and so do the FRIENDS.
Back in 1993 when I did a charter freight weekend, I went into the shop and saw the guys finishing the paint job on caboose 0503, and they had the stencils on the dark redbrown paint, and were putting the white on. Looked great!!
The FRIENDS of the C&TS also do a lot of letting on freight cars so they should have some as well. If nothing else I am sure they could make you some templates to work from. I would hope the groups would be willing to share stuff like this. Of course you might have to send one of the Rio Grande cars back as payment
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Greg