water pump
Which type are you looking for? '69 and earlier: cast iron, driver's side inlet; or '70 and later: aluminum, passenger side inlet?
The '69 and earlier comes in standard 6 and A/C 8 vane configurations, the A/C versions are getting hard to come by. In this case I would just bite the bullet and get the Flowkooler unit, #1701, which has 16 vanes to boot.
1957-1970 MOPAR Dodge Plymouth 273 318 340 Poly wedge water pump – FlowKooler Hi Flow Waterpumps (flowkoolerwaterpumps.com)
'70 and later has 2 bearing sizes, the small bearing (known to be problematic) looks like this:
The large bearing unit (early HD and police, later all) looks like this:
The '70 and later also comes in 6 and 8 vane configurations, but HD units are also available with an anti-cavitation plate on the impeller.
6 vane:
8 vane:
8 vane with anti-cavitation plate:
Flowkooler (1700) and others (Holley, Edelbrock, etc.) also make HP versions of this style pump.
Assuming (...) you're using the later aluminum pump, I would at a minimum use the HD version with the anti-cavitation plate. (Rock Auto and others)