Anything is possible with trucks this old. It's very common for hoods, grilles and fenders/emblems and tailgates to be swapped out for non-originals. Even GM did it when dealers replaced the 60-61 hoods with the later versions. Long ago these weren't collector vehicles, they were just appliances. To most people "correct" parts had no more significance than what type of handle gets replaced on a claw hammer.
Another possibility is the truck might really be a Chevy with an inline 6. It's amazing how many people don't know the difference between a V6 and an I6. It's kind of like trusting a sellers description. His idea of immaculate can be wildly different than yours. As Jake suggested, the dash will confirm the identity. Very few people change out the dash unless there is a lot of money and effort invested.
