The marks on the cam and cam tower are true points for reference but be careful about the timing marker pointing over the Harmonic Balancer.
That unit is just bolted on and has a slot to slide it many degrees before or after. I unbolted mine to clean during a recent chain replacement...Didn't think to mark it. Now I'm really not sure what it is "indicating". Some one may have done the same with yours at some time.
So if you "really" want to know if you are at tdc ya need to make sure the piston is at the top of the stroke first, then get a read on the H. Balancer indicator. If it says "0" cool. If it says "6", "6" means "TDC".
My thought was at 300k I probably had stretch and just rolled a chain on for around $115 bucks. Car runs sooo much better even though I thought it was pretty smooth before.
I do like the way you think in regards to rolling the pump to tune it by "ear". Kind of like the old distributor days
