What to do...

Correct! I think suspension tuning and a nitrous specific converter that the extra cylinder pressure won't "blow through" is the next step if that is the intention for the car. A nitrous specific converter usually has to be tight enough that it won't stall effectively for running naturally aspirated. If the 4500 rpm stall converter has anti ballooning plates and is acting tight, I'd get the suspension ready and put a system on it. I'd probably keep the SV intake, too, the torque it leaves off the line may make the hit a little softer when the spray comes in.
That was my original thought with the sv and nitrous... Although I'm not sure the converter has antibalooning plates in it. I didn't really wanna take the chance with a large hit.