How much does the oil pan hold? Does it have baffles or a windage tray?

Sheldon

Tapping/thicking sounds are valvetrain related or headergasket leaks.
Knocking sounds are usualy bearing or sometimes piston-related.

IMO, the moment you hit fullthrottle on the engine from a dead stop is probably when the oil sloshed away from the oilpickup and could have deprived the oilsystem from have sufficient oil (and pressure).
I've had this happen before and my remedy was to overfill the engine by about 7/16" on the dipstick.

Do you have an oilpressure gauge installed? If not, install one rightaway.

As for oil replacement, look at the current oil pressure and decide if you want to go with a thicker or thinner oil.
I would say for a properly rebuild engine you should not need any oil thicker than 10w40 or even 10w30.

Thanks guys. I do have a windage tray and baffles. I will change oil and slightly overfill, and try to do the other things. Does AutoZone carry the scopes? Is 5k rpm really too much? It was still pulling hard when I let off and shifted. I do have oil pressure guage and it is steady at 50 and above as usual and running at same temp.

Harbor Freight has the bore scopes.

http://www.harborfreight.com/digital-inspection-camera-67979.html

I think they are on sale now for $69.99 in the current flyer. I was thinking about getting one...

Myself I would have someone check preload unless it was a significant bang & it sounds like it was which would point to something more severe than the light clatter from preload. If you have 50lbs of oil psi then adding oil will not help it assuming that was it & I doubt it tho an oil gauge can read good but from the convoluted oil path the bearings can still be starved at times which is why oiling mods when going together are beneficial. Bore scopes are nice but pricey & if there was something in the combustion chamber you'd still hear it. After checking preload (if called for) I'd call it good & run it . 5K ain't excessive IF Piston to valve/Piston to head (quench)/adequate valve spring psi all good? EDIT I reread your OP & I think bad lifter(s)/preload/header leak on the mild tapping & the thud was something more serious/seperate

If it's an automatic, check your torque converter bolts.