The stock VR6 block is very stout. Stock rods and pistons will hold in the 4xx whp range.
There are guys running 550whp with just JE pistons, stock rods and ARP hardware.
Currently im completely stock block with just ARP headbotls, rodbolts and main studs. Running pretty stroke at 12k miles with 400whp.
If there is anyhting I can do for you let me know.
We sell ARP hardware as well as anything else you may need in your journey to make more power.
http://www.20squared.com/vr6.htm