Can you tell what model of car an engine came in just by the stamping on the side of the block? Ya see, I have this 340....

3100 = Jan 22, 1970 build date

150000 would make the likely SPD around late october. The tag in this thread shows 8K cars later and oct 30 SPD

They made Darts primarily in that factory. No guarantee it came from a swinger, just most probably with the vin and factory. The VIN stamp and build date make me wonder.
Hammy and this factory made Dusters with Windsor producing fewer.

The earliest Duster 340 in the list I saw was 179xxx

My Swinger is a 179xxx with a 11-69 door sticker and a Dec build date on the tag. IIRC the engine is a few days after the SPD. I'd heard that they had issues in that plant with getting 340's and the production runs got jumbled up a lot. Maybe it is a Duster as the SPD's may have been done in batches and then when they got the line going, possible delays with the Duster line, spit out some of the early vin/spd stuff in Jan.