318 Build on a small budget
I myself wouldn't do Magnum heads unless there redrilled for a LA intake. Also watch the total lift with the new rocker ratio. The LA is a 1.5 vs. 1.6 of the Magnum.
Good cam recommend since it will not need a converter with more stall.
Your next step after that is more gear. 3.55's would serve you well.
And I have to agree with the Comp Cams Dyno sim cam selector. Cool item.