A big difference between the SN-60 type Paxton, as used on the R2's, and 
the VS-57 McCulloch, as used on the Golden Hawks, is the output shaft.  An 
SN-60 output shaft doesn't "pilot" in the end of the input shaft the way it 
does in the VS-57's.  There's a change, to limit the oil flow out of the end 
of the input shaft, that goes with it.
  A small difference is the size of the fitting in the volute, for boost 
reference to the fuel pump!  It's 3/16" on VS, and 1/4" on SN.
  Jim Moody and I put together a chart of the Stude and Paxton McCulloch 
part #'s for each supercharger part, a few years ago.  It's at: 
http://www.vs57.com/indextech.htm .  See "Parts Interchange", "VS57/SN". 
Sources are listed.
  I found a lot of surprises, comparing part #'s.  Oil pumps, and all their 
parts are the same for R2's and Golden Hawks.  All the ball drive parts, 
except for the output shaft itself, are the same.
   By the way, the Paxton part #'s for the drive balls and races, shown on 
the Stude blueprint for the Avanti, are the old McCulloch #'s for American 
made parts; not the better quality German.  Of course, it's possible that 
Stude and Paxton upgraded parts and didn't change the part #.
                                                               Mike M.