The 10W-30's a bit thin,especially if it's burning oil.
How much do you go through?
If it's less than a litre for every 4 tanks of gas, you may be ok.
If it's a liter per tank, and there's a nasty dark cloud behind you, then not much gonna help that other than a rebuild.
The heavier Castrol was the best I ever experienced in the 2.6L.
And even a re-build will need to deal with the carb controls.

Check which carb you got, it is extrememly important.
If it's the Mitsu carb (made by Mikuni), you have a chance...
Any missing hoses and bits can probably be found from a wreckers in WA. But it's of no help if it's not the Mitsu carb.