You could find a decent redtop if you search hard and have patience... a 1.6 from a gsi will still need wiring looms swapping. If you are swapping wiring looms then you may aswell go with the 1.8 z18xe astra engine. It weighs the same as the x16/c16 but its 100kw straight out of the box. And a hell of a lot more common than the 1.6 engine so parts etc are cheaper. You can pick up an engine with under 100,000kms for $500.
Good luck with whatever you decide