I believe the 323 had a F-series tranny. If you decide the ratios are better you may be able to swap the gears into the G25MR. Oh course get an upgraded clutch and resurface flywheel. I did remember that the G-type had a stronger case which minimizes flex and disrupting the internals. Synchros should be changed since most people that aim to put 250+hp on the tranny bang through the gears with a super short shifter anyway. Don't expect long life from any tranny that you drop the clutch at peak torque or peak horsepower then rip through the synchros. Adding a MS LSD will help matters with traction.