How do 318 powered A-Bodies do in NHRA PURE Stock?

You need to clarify if it's "Stock" or "Pure Stock" you are interested in. Either way, you are limited to the engine specs outlined for the year you are claiming the car in. Besides the group mentioned earlier that has a "Pure Stock" class, IHRA also has a place for it. But the rules are pretty "pure" with a few little exceptions.

"Stock" in NHRA and IHRA is a whole different ballgame and, as pointed out, can be VERY expensive. There are some obscure combos that racers find that can run pretty far under the index. But the HP factors that the sanctioning bodies assign to them, not always the factory rating, can be changed by them to help even things out. But if you can get it to run at least a little under the index specified for the class you are in, you are competitive! (Index is the minimum performance requirement tht each class has.) In other words, if your index is 13.05 and all you can run is 13.25 - too bad, you get dialed in at 13.05. You can dial faster than your index. Just remember that it's basically a bracket race besides the qualifying and if you should end up running against another car in your specific class. Then it's heads-up!

Inkjunkie - the class you are recollecting may have been Super Stock. I recall Ed Hamburger use to have spacers for intakes, but he actually used Chevy small block intakes on his Mopars! But that was before we had a wide variety of good racing intakes to choose from. It definitely was not allowed in "Stock" at any time and I'm pretty sure it hasn't been allowed in SS for quite a while now.