stickers can be easily changed/removed - yes a dealership would have you confirm the original engine installation by the VIN
Oldsmobile 403 (VIN code "K - 6.6 LITRE") was 1977-79 ONLY & the ONLY Pontiac 400 available 1977-'79 (VIN code "Z" - T/A 6.6")
T/A SHAKER stickers originally:
6.6 LITRE = 403 Oldsmobile
T/A 6.6 = 400 Pontiac
1977-'78L78 Pontiac 400 - automatic ONLY
L80 Oldsmobile 403 - automatic ONLY
W72 Pontiac 400 - automatic & 4-speed (W72 "Performance Package")
1979L80 Oldsmobile 403 - automatic ONLY
W72 Pontiac 400 - 4-speed ONLY (W72 "Performance Package")