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Not sure about TDC but the one you are tightening should be on the low spot or base circle on the cam. So not pushing on push rod. No lash to worry about with hydraulic lifters.
Doesn't' matter about TDC at all.
When I did mine though, I found it a little tricky to seat the push rods properly in the lifters because of the angle they're at to the rockers.
I ended up using a pen-light to get it right.