I'd honestly say you are closer to wasting your time than making 350 HP with a 326. Unless you want to spent $6k+ US .

If it's a numbers matching drivetrain, consider pulling it for a 400 or 455. (and keep the original for a future Owner)

That would be better $$ spent.

If it's an unmolested car, keeping is all stock would hold the value much better. Keep in mind, with more HP and displacement, then you will notice how bad the front suspensions are on these cars and you'll want to spend even more money on that, then brakes, then more... etc. Not to knock your idea, but these are cruising cars, not street racers.