FS5R30A is the heavy duty Nissan gearbox used by RB26, RB25DET and Skyline 4WD applications. It is stronger and heavier than the FS5W71C used by RB25DE smaller engines.
Overview
30-series are common upgrades for applications over about 250rwkw when you really need to upgrade from a 71C for reliability.
30-series box vs smaller 71-series
Nissan gearbox codes F = Floor Shift S = Overdrive 5 = five forward gears R30 = gearbox series A = first revision
Applications
JAPAN R32 Skyline with RB26DETT R33 Skyline with RB25DET, RB26, OR 4WD R32 Skyline with RB25DET or 4WD R50 Terrano D22 Datsun Truck with QD32 AWC34 Stagea with RB20E,RB20DE,RB25DE,RB25DET WC34 Stagea WD21 Terrano with VG30E Y60 Safari with RD28T