gnarlyman....I think maybe I was one of the guys you asked. Sorry for the delayed response.
To the best of my knowledge, an M4 serial number on the BB shell means Pro Raider. But the easiest way to tell is to look at the stamped brake bridge.
The word HUTCH on a Pro Racer will be very crisp with the corners of the letters touching, while a Pro Raider will have a more "bubbly" look to the letters.
This picture is from Johan(VBMX member: JJR)'s website and it shows the serial number like yours as well as the brake bridge. This is a Pro Raider:

This picture (below) is a Pro Racer brake bridge. See the difference in the letters?

Also, look at the 'vent holes' in the loops of the Pro Racer pic. They are clean, drilled holes. Now look at the Pro Raider loops - they are 'punched' (see the Pro Raider pic).
I hope this helps....
Tom
[ August 02, 2007, 01:03 PM: Message edited by: Keep_It_Warm ]