Oil Pump Replacement

[cleszkie]

My rear main seal is starting to leak, so I while repairing that I figured I would replace my oil pump as well since the oil pan will be down. My oil pressure has been slowly going down over the past 15 years due to normal wear and I was thinking about throwing a high pressure/high volume pump in there to help get the pressure back up. Went online to order one and found that there are a ton out there for the chevy small block with different inlet sizes and pressure controls. Does anyone have a recommendation for me on which pump to get, what pick-up I need if the stocker isn't reusable, and if I really need the oil pressure spring adjustment?

Also, what diameter is the stock oil pump inlet? Thanks.