i have the pinion snubber out of my eibach drag launch kit sitting right here...if anyone wants it ill give it to em really really cheap...
email or pm me
400rwhp is ok on a stock block...its all in the tune...
500 is the normal limit on a 5.0 block...we had a car(now sold) that had 550rw for over 2 years on a stock block but was tuned correctly ;)