When I did my diff up-grade. An OS Giken diff, Z1 diff cover, SPL diff bushing, MA Motorsprts diff cooler. I installed a SpeedHut Diff temp gauge.
MA Motorsports Diff Cooler Install
It takes about 10 miles of driving to start to see the diff temp gauge moving up. Driving 9 hours at 80 mph to ZDayZ. The highest temp I seen was 260F. Trackday was 270F. I can turn on the diff cooler and drop my diff temps below 200F after about 10 minutes.
Can't wait to see what you get for the tranny temps. I thought about installing a tranny temp gauge.