A very brief overview.
993 rs = 300bhp, varioram with hydraulic lifters
cup = 310 bhp, No varioram, solid lifters (as per 964RS) & higher CR than 993RS, different cams and induction/exhaust system.
RSR = 350/360 bhp. uprated race spec barrells & pistons, solid lifters, no varioram,,,different induction & exhaust system often run with restricters depending on regulations, heard outputs quoted from 340-375 bhp.
Chances are you could find RSR's in different specifications, depending on the event they were last run in or developed for!
You should ask PaulMc, the guy selling you the engine, he certainly knows his cars , also PaulH (obviously).
Surely you want a 964 engine with 265 bhp and a restricted 220kmh gearing in a 964 cup-a-like?