Steve, I am located in Pinjarra, just south of you. If you get stuck with the welding / repairs of the chassis let me know. Got the gear here to easily do that job.
As for the engine, have a look on Ebay. New Briggs engines are not that badly priced. I have considered this for my mower, for when my old Briggs dies. However because of the different shape to the newer engine, you need to modify the handle bars with a spacer between the bottom of the handle bars and the chassis. As the newer engine will hit the handle bars.
I would have a crack at getting the old engine up and going first, unless the output shaft as mentioned before is badly damaged.
Jarrad
