253/308 carbs and aircleaner Q's

[Absinth]

So for a HZ with a build date of 11/77 It should be something like:

1705728x??

No, should be 17057294 and date codes (2707 through 3007 approx) assuming your engine date code is around a month before your cars build date.

[stickthis]

No, should be 17057294 and date codes (2707 through 3007 approx) assuming your engine date code is around a month before your cars build date.

Ah ok so the 2nd to last number is month? I assumed (read elsewhere maybe ebay) that the 2nd to last number was 8 = GMH. not right maybe?

[HK1837]

The second to last number is normally 8 (meaning GMH). Some carbs don't have the 8 though like late HQ auto 350 and early HK 327, but most do. You also see the 8 code for GMH on late HQ 350 auto engine numbers on the end of the assembly plant stamp. Earlier stuff were H5 or H.
Don't worry too much about the date codes. I've seen them 6 months or more earlier than the car and engine.
In general for 308 carbs HT and HG are 702, HQ-HJ 704, HX-HZ (and ADR27A HJ) 1705. Most WB I've seen are also 1705.