Best way to torque crank bolt

No, put nothing down the spark plug hole...
If you have to, I think the best way would be to brace the crank with the hammer handle or a block of wood. You should not need locktite on the crank bolt. (other makes yes, Mopars, no)
You should be using a dampener installer, and then torquing the bolt with a torque wrench. Although in the past I have also been guilty of using the crank bolt to pull the dampener on...
The easiest way I've done it is after the balancer is seated fully with the installer, put a couple small bolts thru the pulley bolt holes, us a large prybar between the two bolts to hold it while you torque it with the torque wrench.