Remove all the spark plugs so you don't have to turn against the compression of other cylinders with your breaker bar.
This is not true for all motors/cylinder heads but with a stock headed small block mopar you should not have to remove the rockers to prevent the valve from hitting the piston stop. Somebody chime in if they think this is not correct.
It's not a bad idea to unhook the battery cable to prevent accidentally cranking the starter with the piston stop in.
Remove the piston stop as soon as you have your marks so you don't forget it's still in there.
Watch the tdc mark on the balancer so you know when you are approaching your stop.
Use a light touch with the breaker bar.
Get a small narrow flexable tape measure Like a what is known as a "stagger tape" in the circle track world to measure your marks.