I have a viking here with a 40" deck that i could wreck.
Not sure what the abreviated model is. 12.5HP with a 5 speed transaxle.
Sticker on the back says Murray made. Best i can work out from the date its a 2000 model. If it is its had a hard life.
38717X53A
Year 00143
The deck is still ok but a bit beat up and some surface rust. Damaged where the discharge chute bolts on, but thats easy fixed.
Even though the pan of the deck might be right, you might still be missing hardware.
I have a 2000 model MT433H here, the pan is the same between the two but this one has the height control in the LH guard and the PTO lever out the right of the console/bulkhead near your knee.
The older model has the height control mounted off the deck on the RH side and the PTO is a lever up out of the console like a hand throttle on a tractor.
You being in Brisbane might be an issue as freight is not cheap.
Might be a good idea if you could take some pictures of your machine. Under where the deck goes as well to show the PTO and height adjustment. No point looking at buying a pan if you need all the tricky bits to mount it and make it work.