Here we are Earl!!!
With the help of Roger Hogan, we made several of these plates. Unfortunately for us, the way we were doing it was very labor intensive, and was not really worth the time for the money it received.
To the Nitty Gritty:
The plates we made were directly copied from the 463. They were 18 1/4" wide by 10 1/4" tall. The half round trim was 1 1/2" wide and 3/4" thick. Numbers in the middle were 5 inches tall. To the best we can tell, a few (two or three) of the K-37's also had this size number plate. The rest of the '37s plates were 1 inch wider. As for the 2 digit numbers, I do not know the specifics, but I assume them to be not more than a couple inches narrower.
The standard set of numbers the D&RGW uses, if scaled to 5" tall, will not fit in the number plate. Front plate numbers are a slight bit narrower in width than cab or tender numbers.
Casey Akin