you get the gear oil and ask mechanic to check if any seals are leaked to change them also coz gear box will be out and radiator and air intake etc so more space to check down and middle of engine.
make sure he fits back every hose tightly. when he says ok done then do start it and then talk with him. let it be for sometime, before moving check temp guage and other normal things, if find any symptoms prompt ur mechanic.
then do let us know how did u feel its ride after it.