Replacing 302 heads with magnum heads

You ever see this article?

Mopar 318 Engine - Car Craft Magazine

Might not be your build, but it's worth a look for perspective...also google "junkyard jewel 318"

If you're 318 has good ring seal and compression, I personally would recommend the swap as long as you make sure the cam doesn't cause issues with the extra lift...but that is ONLY my opinion. 318 owners have been doing this swap for years, and as far as I know, happy with the results. I know my stock 5.2 with a 4bbl makes me happy...