550 injectors and a walbro 255 or a gtr pump. Z32 afm etc. Common mods for 400 on a budget. However 2 inch exhaust is quite restrictive. Best go for 3" at least. What ecu/engine management are you using ? there is a mega thread on SAU forums about dyno results/mods on rb25s. It's a good thread give it a look.
https://www.sau.com.au/forums/topic/55845-rb25-turbo-upgrade-all-dyno-results/
If this is any use/interest to you. I'm in the middle of building my rb25det neo. I'm running Holset HX32 hybrid. Denso 550cc injectors. Splitfire coilpacks. Greddy plenum. FMIC. Greddy boost controller. Turbosmart 38mm gate. AEM wideband. 4" down pipe and exhaust. NIStune ecu. 4" intake with R35 GTR MAF and other supporting shit. Standard internals and head. Will make 450-470hp. Will probably do circa 550hp with built bottom end on that turbo but I'm not looking at that yet.
Hope this helps