If the block can be documented as original to the vehicle, swapping it for another one, even a "year-correct" 283, will drastically devalue the car. I'd do anything necessary to retain that engine, even to the point of re-sleeving all the cylinders back to standard bore if necessary. OEM 57 283's were notorious for cracking piston skirts. Don't get greedy on ignition timing! The problem was with the design of the pistons, not the engine, so replacing the pistons with something like hypereutectic cast ones solves the problem.
Jerry
