To build a 318 is a waste of cash in comparison to building a 5.3. The 350 has 50+ years of aftermarket support whereas the 318 HAS about the same amount of options, your looking at an exponential increase in cost over a comparable 350 in terms of power/reliability. There's a reason 80% of the 318's made found their way into boats going into the 70's. They make better anchors then the Chevy blocks did.
By all means go for whatever build you want. I myself axed the plan for a 318 superbee swap when I started comparing build costs to the numbers coming out at the flywheel. So I converted it to marine and now it's in gramps old glastron.
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