Hi Graeme
I don't have a fuel tank like that and I don't know what is interchangeable for that engine. I would think you would need to be mindful of jet sizes if you put a different set up than the original as your engine is 5hp.
Do you have any mower shops in your area? you never know what they may have in the way of second hand parts and is always worth a try.
Cheers
wce