Tag date looks like "B23", in which case Nov 23, 1966 would be its scheduled production date.
New models generally start late August of the previous year, in this case 1966.
273 was the biggest SB for '67s.
Yes, ft seats are from something else, no highback buckets in '67.
FWIW, arguably the least popular Brracuda body style, but some folks like them.