The waterpump is stock for that motor.
Don't just assume the water pump is right, Neshkoro could be on to something there. How do
you know it's right, just because an Auto Parts store sold it to you doesn't prove it's the right one.
If you have a borescope, you could pull a hose and check the impeller I suppose. There have
been lots of guys assume they know .... including myself, we are all guilty of it. Just try to deal
in facts and not assumptions. Maybe the impeller is loose and not turning like it should.
I'm not
trying to criticize, just wanting to help.
A four row radiator should have NO problems cooling a SBC, something is wrong. Has this car
ever cooled properly, what's the history, anything changed recently.
They make timing tapes that can be installed on any balancer to give you the total timing. The
outer ring on a balancer can slip, so you really need to confirm TDC, then apply the tape.
https://www.summitracing.com/parts/sum-161589/overview/
Try revving the engine while you are outside the car and can see if the lower radiator hose is collapsing?
Thanks for the idea Neshkoro !
I realize that finding TDC is a major undertaking, so yes, start with the fast and easy things first. But at
some point, you will have to go there if the problem still exists. Let us know what you find and
Good Luck !!!