vauxhall corsa 1.0l y reg comfort?

i've been having troubls with my y reg 1.0l corsa comfort, i changed the head gasket and all the seals, but i think the mechanic i took it too changed the cylinder head to an older one, a 2000 one , it didn't fit on the manyiofold?? so he blocked one hole with a metal plate of some sort, and he told me the airflow sensor is broken, i took the car, fitted an airflow sensor, the car started jerking , dissconnected the sensor the car runs ok, it just ruttles allot and drinks allot of fule, now i have a bit of oil leak. i took it back to him and he refused to take it back in, i took it to another mechanic and he told me it is the timing chain, now i am lost and i don't know what to do, any advice? thanks