Sooooo, is this a 1973 /6? I bought it from a guy who said it was pulled from an '82 Van. It had a dual pickup distributor, tons of smog stuff and 5 freeze plugs, but still uses spark plug tubes and has the 280XXXX block casting number.

I bought it for the 4 speed that was attached to it, but now I am curious since it is not what I expected...

Stamp is: 3W 225 4521 (the one is actually upside down)

The blue paint on the head and block strongly suggest an earlier motor was swapped in. If the head has spark plug tubes then at the very least an earlier head was swapped in. Do the rocker arms have adjusters?

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Casually looking for a Clifford hyperpak intake for cheap.

Dan might have a bit more insight as I have not seen a stamp this 'terse'...

225 is usually the displacement... W sometimes is noted as the Windsor plant

If the 4521 is per the chrysler 10000 day calender... the magic decoder page says that would be Dec.13, 1973...

another fun 'check'... would be to look down by the oil pan rail on the block on the passenger side and there might be another pad... what are the letters and numbers stamped there upon?

(If it exists...this is usually the last 8 digits of the VIN for the vehicle it came out of)... so if it's a 1973 it would be stamped something like C3xxxxxx... sadly it never has the first 4 so we won't know what make and model it came out of...

OK, yes, it has adjusters on the rockers. No, it does not have any numbers stamped in the rear deck. Clear pad.

Interesting the massive variety of marking schemes present over the years and plants...

3: H'mm, this shouldn't be here.
W: Built at Windsor engine plant (Canada)
225: Engine displacement, 225 cubic inches
4521: Built on 13 December 1973

This stamping is not consistent with what "should" be there, in quotes because it's not uncommon to see variance from the published stamping breakouts. A model year 1973 engine should have a J as the first character. And in December 1973 they were building engines for 1974-model vehicles, not 1973-model vehicles, so the first character should actually be a 4 (1973 was the last year for that kind of letter coding of the model year). So given the engine build date of 4521 (13 December 1973) what most likely happened was that the stamp operator accidentally stamped "3" instead of "4". Your stamping would be completely consistent if it read 4 W 225 4521.

1974 was also the last year for the head wth spark plug tubes. 2806830 is the right block casting number for a 1974 engine., too, and Slant-6s were painted blue in '74, so no inconsistencies there.

Looks like you've got a slightly mis-stamped 1974 225 engine.

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Too many people who were born on third base actually believe they've hit a triple.

Not on the rear deck, there is a pad below the oil pump, toward the rear of the engine where the oil pan bolts to the block...