Yeah do a tune up (plugs,wires,cap,rotor,o2 sensor, fuel filter, air filter, and pcv) and you should be ok unless there is something really wrong. Also since the motor was swapped make sure all the vacuum and egr lines and stuff are all hooked up right. I run synthetic and I found it did help the mileage quite a bit. I get 18-20mpg on my "average" tank. I have seen it creep up to 23 or maybe higher on the highway but it's been a while since I did a whole tank highway trip.
Oh ya try to keep the rev's under 3.5k and don't go much faster than 110km/h on the highway.