SB push rod legnth checker, how to

No, do not check lash at TDC. Either use the Mopar chart or the "EOIC" method

Either method insures that the lifter is on the backside (heel) of the cam, which does not happen at TDC

When the EXHAUST valve starts to OPEN set the intake on that cylinder

When the INTAKE has opened and is nearly CLOSED set the exhaust on that cylinder

The chart, which requires you to mark the balancer every 90*