I managed to dig out my Stash of standard ones of these.
I have to admit to two things:
1) My name is Nasher, and I'm an Exhaustflangeoholic.
I found 7 of them in my box of engine bits and pieces
2) And I don't know how I missed this, all 7 have a small chamfer on them!!
I obviously decided when I drew up my Ali ones that it was not needed, and the one I looked at the other night has a very very small chamfer on it.
I measured them, and all have the stud holes at 62mm centres.
The range of diameters for the recess where the collets go is between @52.8mm and @53.7mm.
Interestingly the pair in a separate bag that came off the M900 had smaller Chamfers, and recesses closer to 53mm than 54mm.
As a pair they also appear to be a slightly different outer profile and made from a different steel.
Oh, and I'm really liking the finned ones fitted by Dukedesmo.
Nasher.