The numbers on my transmission were 2" high, 2-3/8" wide. I downloaded for free the font Placard Condensed (not Placard MT Std Cond which is similar but not as correct) and made a master "602" with numbers 2" high. I think the rubber stamp needs some margin around the perimeter, so it needs to be slightly larger.

At RubberStamps.net, I uploaded my master and ordered a stamp 2.5" high x 3" wide, part number WOODSTAMP77, about $24. This is one stamp with three numbers, which is better than three stamps of one number each..

Because the margin around the rubber part of the stamp in the last photo seems unnecessarily large, it looks like maybe I could have ordered a smaller stamp 2.25" high x 2.5" wide, but I don't know if that size is available.