oceancrosser:
I donīt think Boeing "removed EPR" from the 737 Classic. Rather they chose an engine, CFM56 that used N1 as primary power parameter in line with GE philosophy. The CFM56 predates the 737 Classic by almost 10 years.
And the CF6 used N1 when it first flew on a B-52 testbed - late 60s.
http://www.aviastar.org/pictures/usa/boeing_b-52.jpg