Headers vs. Manifolds

Based on the BBD article I linked above, only a 440 or other tall blocks need angle milling to fit. Not saying it doesn’t require work, but doesn’t sound like it would require machine work.

Personally, I would buy the available manifolds, bolt them on and see how it feels. If you need more power after that, save up for headers and when you swap them, sell the manifolds for at least what you paid for them.