If the body was on the westbound side, that would indicate someone driving from the Philadelphia area put the body there.
Now why, after killing Corriveau, would a murderer move the body and leave it where it would be highly visible along a well traveled highway.
1. He didn't have a wallet, but he had fingerprints. Even in 1968, fingerprint evidence was well known.
2. The area around the Downingtown exit was either farmland or wooded in 1968; some of it still is. If someone wanted to dump a body, those areas are far better and they are within three miles.
Corriveau's face was covered with a pea coat. It is customary to cover the face of a dead person as a mark of respect. Further, the body was placed in a partial sitting position and, it is unlikely that this was a random position.
Conclusion: The person who placed the body there, wanted it to be found and was not concerned if the body would be identified. That Corriveau wasn't identified for decades was not part of the killer's plan.