That looks like the eary set up, with the "y" going into the throttle bodies, and the intercooler piping from the turbos to the intercooler running inside the engine bay.
Tturbos should be GT35Rs(61 mm) T3 with a .58 AR.
Plugs: Autolites 3923 gapped at .028
The switch on the console is a hi/lo switch. On my original set up there was a manual boost controller under the passenger dash that would control the boost setting for the HI switch position.
there were some marking on the knob to more or less get it to a 12 lbs, or 15 lbs, setting.
With the switch off, the car would be on Waste Gate Springs. Mine was on 6 lbs.
The 850 rwhp depends on boost setting, on a stock motor on my car it was around 14 lbs, and it needed race gas.
Pump gas was 650-680 rwhp on around 10 lbs., again this was on my 97 GTS on a stock motor with the same turbos, but the dual piping set up to the throttle bodies.
Although those turbos don't have great top end (party is over at 5500 rpms), they kick hard as ****!!
I remember the first time I got into the throttle on mine, coming from a 780 rwhp Vette...
I totally freaked out, and got out of the car shaking...