3/16" tall stamped numbers ain't going to be very impressive and barely readable.You could get a letter/number stamping kit and stamp your own:
http://www.harborfreight.com/36-piece-1-8-eighth-inch-steel-letter-number-stamping-set-800.html
Spooky Tooth Cycles originally had the 49cc stamped cover then they were bought by BikeBerry who is sold out now.
I have some higher end billet clutch covers with 48cc engraved in a few different finishes.
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