If you have had a problem safely balancing a transmission on your transmission jack then consider this solution known as Squangle Bars. The following illustrations show how they work.
First, remove the standard chains and blocking devices and position the jack as usual.
Third, install the Squangle Bars as shown. Be sure the trans jack plate is lifting the trans slightly, then tighten the pinch bolt joints.
The adapter is very stable even on heavy and awkward loads like this transmission transfer case assembly from a Ford truck.
Second, remove the transmission mount and bolt the L-Blocks of the adapter in its place.
Lastly, remove the trans as usual; you will immediately notice the transmission is held more solid than with chains, blocks or straps.