I’ve got to think that starting with a standard st would be your best bet. They can be had very cheap, some basic repairs might be needed. The brakes and suspension would be capable of handling the power.
The only reason I can think of someone wanting to put the engine into a 1.6 car is that they can’t afford the insurance on a genuine ST. So they will be yet another uninsured driver on the road.
Save your money buy the car and insure it.