Have you contacted Dynomotive or HPHeaven? They are business over in Australia that know these motors inside and out and have custom pistons, rods, cranks, camshafts, you name it. I've been talking with Mark from Dynomotive for a little while. Flatlander Racing can make a custom set of pistons and rings in Forged for about $750-$800 here in the US and for about $1200 will make a set of billet rods. I've been thinking about doing this engine in a small light car for sometime and turbocharging the wee out of it. You could also look into changing over to a Megasquirt ECU to control the fuel/timing, would be alot simpler/cheaper than upgrading the factory one. They sell something overseas for it but it is $$$$. Good luck with everything and look forward to seeing lots of pics! Here is a quote from Mark:

"Hi Dallas,

I have not seen a s.o.h.c 6vd1 however, I have a lot of experience with the dohc version (would be the same bottom end) I have one here at the moment running 1680hp, the stock rods fail at around 600hp and the stock pistons fail at around 450hp. I can’t comment on the flow of the heads, because I haven’t seen s.o.h.c. but for the twin cam we run larger valves and custom porting, 80mm throttle body and big cams. Even on the mild engine with a gt3582r turbo (700hp capacity) we see around 520 rwhp"