Swapping the engine is no matter a hassle. First of all be prepared for 6 months period for frequently going to the workshop.....but don't be Scared of...
As far as the swap is concerned, I am much happy with the swap...offcourse after a pretty long 7 month time, but in return, it is quite fruitful. Immense power with a very nice fuel consumption(13Km/16Km City/Local Petrol, 130Km/190+Km CNG 60 Cylinder). 100HP/5000 and 145N.m./4300 torque is not a joke either....
Coming to the point, I will recommend you the swap. Parts are not any problem. You an get new parts as well as old parts. Chevrolet Optra has the same family engine A16DMS(1.6L 16V) and due to this reason it has many common parts with its other member A15MF(1.5L 16V) including intake and exhaust manifold, Head, CAM, valves, crank, connecting rods, engine bearings, water pump, oil pump, timing belt, tensioner pully, main pulley, gear box, axles, CV joints. Majority of the sensors is common like TPS, CTS, IAC Valve, O2.
It differs by few things including the Air Fillter, Pistons, plug wires, engine wiring and ECM. Getting these items is not any problem, since they are in excess with the old part shops at Islamabad/Rawalpindi, Lahore, Karachi and Peshawar.
It will require no alteration in the engine bay, will utilize the existing gear box. Just a bolt-on job. I spent around Rs.40,000/= on the swap, utilizing the existing block, but changed every bit, and offcourse complete overhaul of the engine block (head was in a good condition).....