I also have a '55 date code engine with casting #2324002. It came from a '55 or '56 Blue Chip (same series as task force Chevy). It is stamped 248. That casting number isn't listed on the Inliner's list. And as you stated, Blue Chips weren't supposed to have 248s. My theory is these are replacement engines. Replacement engines came with no serial number because vehicles were titled by engine number. The common practice was for the mechanic to stamp the engine number from the old engine onto the replacement engine. I have no idea if mine is really a 248.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.