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How much more work to the block is required to run the 4.15" vs the 4" crank? Obviously rods and/or pistons have to be different and will be more expensive, but I wouldn't mind hanging a 426 badge on the hood and have it be truthful.
Look into shorter Chevy aftermarket rods for a 2.100" rod bearing, or even 2.000". You can then grind the crank journals down and even offset grind them to adjust the stroke a bit and/or piston heights. You might have to narrow up the big ends of such rods a bit.