If you can do all the fab work your self it will work out heaps cheaper than a 4AGE conversion because you wont have to worry about all the EFI gear. And trust me a 12A will have alot more torque than a 1.2 piston engine. If its a weekend car id recomend going for an engine with some pretty agressive ports (PP or BP).

Oh and the whole reliability thing is BS. If you take care of your engine it will take care of you. People always complain about reliability, but I've got a 300BHP 13BTT it will easily last 100,000 KMs id like to see how many people have done that with a 4AGTE