In the early-mid 1970’s, Boeing was looking towards a new generation of wide-body jetliner to replace their older planes such as the 707 and 727. Initially designated “7X7,” it eventually became the 767. Along the way, a wide range of unusual layouts were studied, a number of which were built… at least as display models.
This concept called for four turbofan engines mounted above the wing. This would add two features:
1) It would be quieter, since some of the noise from the exhaust would be shielded from the ground by the wings (though potentially louder in the cabin)
2) The Upper Surface Blowing configuration creates additional lift at low speed due to the Coanda Effect.
On the other hand, having the exhaust scraping directly along the wing surface would create additional stresses as well as reducing thrust at high speed. Additionally, a configuration like this would be difficult to re-engine later with higher bypass engines.