I always set the dist to tdc before I pull it.
And verify that the piston is actually at TDC before you rely on the timing mark.
That way you know that you dont have a bad balancer.
Looks like you know about the oil pump drive spinning out of sync when you pull the dist.
I have a big monster standard screwdriver that fits into the hole and doesnt bind and I can eyeball how far I need to turn the oil pump in order to get it to drop right in.
Everyone has a favorite method for stabbing a chevy.
I look at it this way,
Setting TDC involves leaning over the fender and leaning over the radiator.
Stuffing the distributor involves pulling the throttle body studs so you dont impale yourself and crawling over the whole thing while hating the world.
All kinds of things can go sideways while stabbing a chevy
Especially if you are using an aftermarket dist.
Pull all of the plugs.
This is so you can turn the crank by the snout bolt without breaking it.
Set it at TDC and verify it before you pull it.
Make sure the piston is actually at TDC and not that the timing marks are off.
Pull it, turn the oil pump drive back a bit and stick it back in.
If it doesnt line up at TDC turn the pump a bit more.
It will only be off by one tooth.
Stab it.
Pull the coil wire and unplug both injectors.
Roll it over a few times
See if you can turn it back to TDC without turning it backwards at all and see if all of the timing marks and the roter line back up at TDC
That will tell you if you have timing chain slop.
If it does all line up again.
Probably good.
Now, again with all the plugs pulled,
You can rock it back and forth with a breaker bar on the crank bolt and kind of get a feel for how much slop is in the timing chain by looking at the rotor and how far you need to turn the crank before the rotor turns.
Keep in mind that when you turn the crank bolt counterclockwise that can loosen the bolt.
That is why you need to pull all of the plugs.