Rare Flywheel

Can you elaborate on what you mean by a "rare" flywheel? That casting number, 2264598, was used over a wide range of years and applications, and was balanced differently dependent on it's ultimate part number and application. Any idea what it came from? That casting was found on everything from 318s to cast crank BBs. Looking at the balancing holes, my guess would be an internal balance engine- 360s had (3) 15/16 holes drilled closer to the hub, cast crank BBs had a "scallop" flycut into the outer rim of the flywheel, and I don't recall the cast crank 340 balancing scheme but it was a different layout yet again... Without a history or part number my guess would be 318 or '68 through early '72 340, internally balanced. Just my SWAG.