For GpA racing /Rallying a 9" Diff was used. If the Diff you are talking about has a 7.5" cwp then its a GpN diff ! These use the std v.c in various states of tension and 909 Motorsport Cwp's in various ratios. The 7.5" and the 9" share the same "shoulder " width of 7.5" tho , so be careful to get the right one . As for prices, pick one ! Everyone has their own idea what these are worth , generally too much .