I just ordered a Carter new pump for my 1970 400, It appears to have a small diameter cast impeller.
Should be here latter this week.
For testing I also ordered a new separator and sleeve set too.
However, I have never had overheating problems yet, and I'm currently running a small cast rebuilder napa pump.
A "Rodney Red" radiator in my 1980 Firebird.
Very interesting topic though.
Steve
http://photo.starblvd.net/zanko20