have read plenty about this though ........ problem you have is the conrods on 3.0 are the weak point due to their lack of width!
thats why everyone seems to agree on 250bhp being the max for this engine reliably... and cost effectivly....
so as for NOS i did read some guy putting 100bhp through his at santapod so was making in region of 350bhp
on just a standard / mild state of tune engine... prob is how long it lasted i dont know and he did say clutch was no way up to it....
it can prove to be expensive as well as it seems NOS is around the £5 a pound to fill .. average bottle 11lb.. so call it £50 and prob lasta couple mins tops........ my old 325 Msport had 75bhp jets and full to empty in 1min 40 sec's!!!!!!
Dont get me wrong The engine has been tuned up to around 420BHP in a normally aspirated state of tune by Swindon Race Engines though this will set you back £18k + vat