That has nothing to do with an assembly plant. The "B" is the assembly plant. LM23P is the VIN for a true 1969 x 340 Swinger. The L is on the block as well.. just so light you don't see it in that shot. They were still on full VIN's I guess when my Swinger was built. My '69 Bee only has a partial... a 69 Roadrunner A833 I have as a spare has full VIN. Depended on car line and timing as to when they started getting lazy.
