somebody wrote:
A reinforced concrete lintel will typically have a proper orientation.
(ie "this way up"). The structure of the reinforcing requires it.
Basically the steels in the bottom of the beam are under tension while
the concrete at the top of the beam is under compression.

Turning the lintel on its side would result in little or no reinforcing
of the concrete.

Many *pre-stressed* (one brick deep) lintels have pieces of
wire rope running through them in the middle - these should
bear more load "on edge".