Bruce,
The picture of the muffler you have posted is not like the one on my mates mower.It is held in place by two metal clips,one upper and one lower and not by bolts.
With the info that I posted earlier, can you confirm whether it's a Power Torque 160cc engine or not? The engine is black in colour for what it's worth.
Sheriff,
Below is a picture of a power Torque Muffler which will confirm that you a power torque motor.