Alot if people will say that the g4 is better, personally I don't really know but from experience I'm very happy with mine
Not sure what extended crank is :s do you mean extended sump?
I'd leave your head as it is for the time being
That crunch from 3 rd to 4th is a common thing, some people claim they fix it from using Redline gear oil..
Personally I had my box rebuilt with new syncros and a modification on 4th to stop it from crunching in the future
Depending on what sump and baffling you have, I like to fill my sump to around 6.5 liters to stop oil starvation during high G's. Though I do have an after market sump at home ready to be put in for future track work
Injectors ( correct me if I'm wrong here) usually make around the 270-280 mark on standard rail pressure
I'd change my fuel pump anyway ( my standard one got old and killed my last engine.
Also afm Max out at around 300rwkw, but if you get a Link g4 you get rid if them anyway
Hope this helps