I always thought that loop was some sort of anti drain back. I guess it would cool also.

Just for reference, the original rebuilt pump from my core engine ('78 Cordoba 400) with stock repop hoses (NAPA) has been leak and problem free. I turn it with a smaller than stock crank pulley from March to keep speed reasonable with my hotter engine (6 1/4" vs 7 1/4"). I may add a PS cooler but it has been completely happy so far running Dexron ATF fluid so no rush.

I assume your pump is press on pulley shaft?

I have the March Pulley kit with Key way and I think all key way shaft might be higher flow than my stock pump...

Found this very interesting discussion stating that most (if not all) after market pumps have the thicker Cam/Vane pack with 30% increased flow...

http://www.pirate4x4.com/forum/general-4x4-discussion/973826-what-s-going-inside-ps-pump.html

Yes, the one I run is the later OE style press on Saginaw.

The original pump on the car ('70 318) is the keyed shaft Saginaw with big nut. I've got that one stashed away. It can be used on a BB with a conversion spacer from Bouchillon.