What you are looking at here is a very rare beast. Tommykaira M30 based on an R31 GTS-R but with the RB20DET replaced by their own in house special RB30DE. This 3 litre dohc NA 6 started with an Aus spec RB30E block filled with custom goodies before getting an RB20DE head and very nice looking headers fitted. These mods produced 240HP which is very respectable for an NA 3 Litre. Their RB20DET powered M20 only produced 220.
To put those M20 and M30 power figures into perspective a standard R31 RB20DET puts out about 180-190 HP, the GTS-R version 210 and the RB30ET only found in Australian VL Holden Commodores and Calais about 200. The Australian R31 Skyline GTS II with a worked over RB30E put out 190 HP and just fitting an RB25DE head, inlet and coil pack ignition to an RB30E bottom end will match this 190. So the M30 has another 50 HP of go goodies fitted. That exhaust manifold would account for a lot of that.