I'm not expert but just sharing my experience.
1))My 95 corolla se limited is giving me an average of 11-12/l km in city nd 13-14/l on gt road..
2))My 98 se saloon L is giving about 11km/l in city nd 13 on gt road.
Another average to share is of premio 2007, which is quite impressive,,but it does not make any sense to compare that 1.8l car with the above discussed cars.
The cars I discussed above are a/t nd run with ac, on..
Again Im saying that Im not an expert. Experts may guide u better.
As u said that ur engine is not having any problems regarding performance,,I advise you to not to go for the swap. Do the petrol tuning by some good efi mechanic...4afe is not that bad. Its quite powerful and economical one..