Hi Dave (if I may),
http://www.gunauction.com/buy/107853...ut-british-wwi This is an expired auction for an uncut Mk VI to give you an idea (if you look at the photo of the cylinder, you see evidence of the proof markings and the like and look at the side of the cylinder for the serial number). (Mods, if this is inappropriate please delete, but I hope it is ok to show an expired auction).
If the serial number looks like the one in those photos then it should be ok but if some of the numbers are missing the bottom strokes then it's probably shaved. Like Doug said, your cylinder gap looks about right but best to be safe. $450 for an uncut Mk VI would be a steal, I think! But acceptable for a shaved one, too (particularly if you reload). Either way, she's a beauty and well worth having! If it is a .45 ACP, I use .452 bullets (Berry's plated round nose, hollow base) in an Auto Rim case with Trail Boss and she does quite well even though I load quite gently for my 'been through the wars' Mk VI.