Looking at the engine, it reminds me of a mild street tuned motor. The Nissan factory GT-R’s has about 550 hp as I recall but HKS claimed 600 at the time. I think most of this was perhaps how far each team was willing to turn up the boost. You can see the interesting shock tower brace backed by the cage extending through the firewall to triangulate to the shock towers.
Group A turbos were a larger variant of Garrett’s T2 family. The OEM turbos had lightweight and fast spooling but fragile ceramic turbines but the Group A turbos had a bigger compressor and turbine wheels and the turbines were metal, not ceramic. The turbo specs were impressive for the time and very much like what I used on my Z32 back in the day. TO4B compressor housing, 62 trim T3 compressor wheel, 79 trim turbine wheel, and a .64 AR turbine housing. For my car, I just used a .86 exhaust housing. It was cool to have friends at Garrett who could get me these parts. Like OEM the turbos use internal wastegates. A lot of the power increase was due to the turbos. The exhaust manifolds were stock and you can see the nice HKS charge pipes with the anti-slip couplers.
The RB26DETT engine uses a slightly larger plenum Group A intake manifold the feeds the standard ITB intake. The engine has a pretty humungous fuel rail feeding the injectors. You can’t see it but like a lot of JDM race cars, the GT-R as a butt load of fuel pumps, about 4 at least.
The engine is still a wet sump and uses this really cool AOS system to vent the crank and return blowby oil to the sump. You can also see the high-mounted cooling system surge tank with vent lines to the radiator and head.