Similarly to the above post, I use a dial indicator on a valve dropped on top of the piston. Bring the #1 piston to TDC compression, remove the valve spring retainers and spring from one valve. Allow it to rest on top of the piston and use a dial indicator to measure travel. Pick a dimension (I use .050") and rotate the engine one way until the piston drops .050, mark the balancer. Rotate the engine the opposite direction until the piston rises to TDC and drops .050". Mark the balancer. In between the two marks is true TDC.
On another note, it would be nice if someone manufactured a timing pointer and degree tape kit for the balancers on 12 and 24 valve engines... Then a person could find TDC and install the tape and pointer, facilitating much easier timing changes.