The listing would be correct. 1977-1978 Pontiac Models 350cid/400cid Non-California A/T, at least according to my manual. Also, as per the date code, it seems it may be a Service Replacement for that specific carb number.
Ok, so then if I'm understanding you, it is a service replacement for
all 1977 Pontiac 350 & 400, as well as 1978 Pontiac 400 applications with an automatic transmission.
For 1977 the numbers this replaces would be:
17057262 (350)
17057266 (W72/th350?)
17057274 (L78/th350?)
For 1978 the numbers this replaces would be:
17058266 (W72/th350?)
17058276 (L78/th350?)
17058278 (L78/th350?)
I didn't realize that GM ever made generic replacement carbs like that.
Thanks!