The scheduled production date (SPD) will be on the fender tag or build sheet
Despite common belief, that code is neither the date the car was built nor scheduled to be built. It's the date the order number was
added to the production schedule (Production, Date Scheduled). No, I repeat
no Chrysler product was ever built on the code on the data tag. The SPD for my '73 Challenger was 122; it was built February 9th per the window sticker (which I have). The actual build date only appeared on the bottom of the window sticker, which was printed when the car came off the line. There is no way to know the build date without the original window sticker. The last known Hemi car built has neither the latest SPD nor the highest sequence number, but the original window sticker shows a build date of 0731.
It's a long read, but you can learn about it
here. Yes, they even tested the paper on which the window sticker was printed to verify it as original.
In general, the SPD is pretty accurate to within 2-3 weeks.
Last 5 are production #, it is high, I think they only build 31K that year?
Remember, though, the sequence number doesn't apply to a particular model, it only indicates which car it was in the original build sequence (and per the above-linked article, not necessarily indicative of when the car was completed). Hamtramck also built A-bodies and Challengers, both of which are interspersed with E-bodies in the number sequence.
Referring back to my '73 Challenger, that car's sequence number was 3309xx and it was built February 9th. Yeah, it's a different production year but applying some simple math to my sequence/date built versus your sequence, I'm relatively confident the car would've been built more than 73 days after the start of production.
For model-year 1974, a Federal law was enacted that would not allow a car to start until front-seat passengers were wearing their seatbelts. All cars were built this way initially (Ford, GM, and everyone else too), but the law was rescinded fairly quickly, after senators and representatives bought new cars and were annoyed to find it applied to them as well. Apparently they didn't want to wear their seatbelts either. This may have something to do with the date change in the application, but that's just a guess.
If your car was built whilst that law was still in effect, it would've had something like this under the hood originally:
Pushing that red button would allow the car to be started without the seatbelts engaged--
once. After the car was started, it reset itself and would need to be pushed again before the car would start unless occupied front seats had their seatbelts engaged. Anyhow, the override switch changed on
November 16th, not in October, but was still used for awhile. If you have wires coming from under the seats, and from the seat belts, your car was definitely built with it.
It's entirely possible that some of the underhood wiring butchery on your car was because of that idiotic interlock. My Challenger definitely it; the switch is out in the garage somewhere, never to be used again. In fact, I think I ordered a '73 engine harness simply because I didn't want to deal with the interlock nonsense, although it's easily bypassed. I may need to do some re-pinning at the bulkhead, but I haven't looked at it yet.
