The short answer to your question is yes. But it's not that simple, it never is.
The stock block will hold the pressure but it is uncharted territory as regards whether the stock water pump and the stock water passages will cool the engine sufficiently. Racing SVXes have shown this to be a weak area.
To get 500 whp means you have to boost to 500 + 25% to get over transmission losses. This in turn means 22 lbs + 25% or so, which is nearly 30 lbs. For the most part this means you can forget about superchargers, it will be turbochargers only. This amount of intake pressure will need a good special intercooler, as Subaru ones can split at these pressures.
On the positive side, if you change to a 5 or 6 speed you can rev to beyond the 5400 rpm the 500 figure was calculated from. This will make your theoretical max hp figure easier to achieve, particularly with better breathing from the improved cams and valves you are talking about.
If you are actually going for a pressure charge rebuild, then be conservative and realistic about what your max hp
can be, rather than what you would
like it to be for bragging rights or whatever reason. It's OK to dream, but dreaming with money in your hand is a dangerous business.
Better to be realistic about what you can achieve.
You mention above about the cheap route regards different pistons and rods. I respect what you mean, it's reasonable to plan work within budget.
Be very aware
there is no 'cheap route' to 500 whp. It's just not happening.
Best of luck with it. Keep us posted on progress.
Joe
