I have the same setup ( except im bored out 306)and haven't gotten it dynoed yet but i was told i had around 270 - 290 HP and cam probably get 300 with a good tune.
300 wheel won't happen without porting...there was a gigantic thread a couple years back on one of my local forums about an entire group of locals with gt40 heads trying to get the 300 rwhp mark...some made it, but it took porting work.