I'm not an expert on these engines by any means, but, to me, it sounds like some facts got mixed up. I've read quite a few times about putting 318 swirl port heads on pre-Magnum engines, but, not on Magnum engines. Magnum engines/heads were the next step of evolution of the small block head after the swirl port. The swirl port heads helped with fuel atomization and bumped compression up a little. Just the things a smogger LA needs.