Both springs in an R2 distributor are the same.  The "Mr. Gasket" 
kit #925 B is about $5, from Summitt or Jegs.  It's a substitute 
set - maybe exactly the same.

  An R1 distributor used one spring like the R2 springs,; and one 
that was heavier, with elongated eyes.  The heavy spring comes into 
play above 1250 rpm (engine). The light spring controls advance to 
1250 rpm.  The R1 advance curve in the Avanti manual shows a sharp 
break at that point.

  The distributor cams have a plate that the weights ride on. A slot 
in this plate controls total advance.  R1's have 2 degrees (crank) 
more than R2's, 20 versus 18 degrees.  I gather R1 & R2 cams are the 
same, except for the length of this slot, since dwell is the same.  
Two degrees seems trivial, to me.
  R1 & R2 weights are the same.  The bushed, Chrysler weights are a 
very good idea. 

  The R1 spring set is Stude # 1558285.  Prestolite stock # is 50-
214.  Prestolite part # is IGB-376CS.

  The R2 spring set is Stude # 1558286.  Prestolite stock # is P50-
107.  Prestolite part # is IGB-346AS.

  The above Prestolite #'s were supplied by Wayne Flowers, some time 
ago.  Thanks, Wayne!

  Dave Thibeault has both spring sets in his catalog, listed by 
Stude #, for $12.50 each.  He may have the bushed weights, too.
                               Mike