I also call BS on 283rwkw with stock turbos. I've seen 250 odd a number of times. Doesn't really matter anyway unless you are trying to tell us that it's for real. It's only useful to you if you keep using the same dyno and operator as a comparative thing. I personally try to avoid dyno's that are known to give inflated figures because I would rather know the truth - or as close as is possible given the known drawbacks of dynos generally.
That said, with 600cc injectors and the turbos you are thinking of you will be fine to keep the stock fuel pressure.