When I worked on the BAC 1-11 and the 146 was just being mooted, we were told that it started life as the HS681 with twin Pegasus. This was intended as a V/STOL supporter to the Harrier II (P1154) force. The Peggy gives you two effective jets per engine (see the QSTOL Buffalo) so they needed to be replaced by the 4 Lycomings.
Some of the last Western contra-prop research was done by Boeing using a Fairey Gannet in support of the UDF concept - it was curtailed when they ran out of tires! - or so I was told by an aerodynamicist involved. I beleive they found about 10% increase in efficiency mainly from removing the swirl in the propwash (as above).