Hi,
Please read the MOV datasheet:
it says:
* I_MAX (8/20us) = 500A. Can you ensure this? If not then you may kill the MOV
* V_C (Clamp voltage) at 5A MOV_current (yes, 5A only!) = 77V. Can your circuit withstand this? If no then the circuit is still not protected.
My opinion:
For safe operation you need a current limiting device before the MOV. (You need to read the fuse datasheet according blow time vs applied current)
Then you may calculate the expectable clamp voltage.
In most cases you need a second stage for good protection.
Klaus