Upgrading my 340

Your at a crossroads performance wise.
Transforming an A Body into a 13 second car is pretty easy and make for a fun and very daily driver kind of car. But after this every performance gain cost more per hp and cost in the drivablity department.

It seems like your looking for something to buy that will gain you a huge improvement in power beside nos everything is 5-10 hp improvements carb, headers, intake etc...

The only thing that's left to give huge power that doesn't require a complete redesign of your engine would be fully ported heads.

But before I'd buy anything. I'd start a new thread in the racing forum and dial in what you have before trying to move to the next step.

P.S. What tires do you run at the track ??