You can go for the DOHC engine. You need complete wiring along with ECM and for safety new timing belt set (broken timing belt = warped valves). If you need economical engine then you have to arrange new oxygen sensor. Another thing that needs to be arranged is the cielo's suspension (shocks assembly + springs) and brake parts(brake servo+master cylinder) as the engine is quite heavier(+30kg) and powerful (+20HP, +20Nm torque) too. To be on safe side, you have to put a new clutch set. Timing set is available for something around Rs.12K while you have to arrange the oxygen sensor with your own research.
As for the engine swap is concerned, it is hardly a day's job provided all the necessary parts (engine, ECM and wiring) are complete and intact. For latest price quotes, you can consult the contacts page(page-3).