Swap or rebuild?

For a grand you would be much happier to mod what you've got over doing a magnum swap. Normally I'm on the magnum band wagon but I honestly think you'd be better off just doing a simple cam swap (valvesprings also) in your 318, Comp xe268 or similar, and calling it good as far as engine mods. You already have a good intake and longtubes so this would be a natural upgrade. Then take the rest of the money and focus it on the drivetrain. Install a shift kit (Transgo TF-2), get a decent converter in the 3000-3200 range, and install a good aftermarket trans cooler. After that all you'd need is some gear (3.55's would do fine, 3.91 is a bit much on the street imo) and you'd be good to go. If you were to compare this solution to a magnum swap with a stock converter and 2.xx gear, the solution I propose would be quicker and more fun to drive. Plus you'd be more likely to stay on budget.