SR Rolla, You 'should' be able to see 280 RWHP with a black top running standard management and standard turbo, i have a standard s13 SR20DET in my wifes datsun 1200 ute, with factory ecu and 15 psi, decent IC and decent pipe work it ran up 238 RWHP, a 50 zex nitrous kit pushed that to 248 rwhp but really made the difference to the torque (hot side just physically cannot flow anymore i think) the s13 engine has the tiny t25g standard.
With 238 RWHP in a 780kg car it runs consistently into the 12.6s, with more potential as we only use falken 205x45x16" tyres and 60' times are in the 2.2s, i scored a set of used 16" low profile circuit slicks, using the 50 kit from 2nd resulted in 11.9 @ 116, 1.9 60', this is still a factory engine, running factory management, starts first time every time and never misses a beat which i think is bloody awesome :)
I would expect an 850kg car with 50 or so rwhp more would run similar numbers.
You will need atleast a bosch 094 pump, i have tested a vl turbo pump but its not up to the job with anything more than 10psi. Also make sure you tap a barbed fitting into the shifter housing on the gearbox, i have found that they need a bigger breather as without one thay leak past the rear seal.
Here is a Video of the 1200 ute in action.