try giving the engine all a good clean internally. if its all been rebilt then you shouldnt find any nasty side effects. engine oil flush, coolant flush, run some of the 10k boost stuff through the inlet. should give all the internals a good clean.
if the engines a bit ropey then i wouldnt go as mad, i tried the oil flush on my nova and its helped the headgasket on its way, unpluggin all the holes.

also when they checked the pistons did they check the rings.

chris