273 with no stamp

I just purchased a 1965 Dart. It's a 273 car and the engine is also a 273 but the block was cast on 4-1-1969 and does not have any stampings either on the front of the block or down on the rail.

The heads and manifolds all appear to be correct for the car. So my theory is that the short block was replaced under warranty in 1969 or 1970.

Does anyone know if my theory is plausible? Would it be normal for a 1969 short block to be devoid of stampings if it was shipped to a dealer's parts department?

The block casting number is 2806030-273-3.
Author: 65DartGTConv