Build what you have and budget allows is what I believe.
If I'm to question the reason for a 318 or 383 build then I would say, why waste your money on a 408 when for the same amount of money you can build a 512. lol
Less money! 440source has full rotating assemblies that start at $2K. For the price of cylinder heads, B/RB vs SBM’s, the power return makes SBM’s look like a bad choice.