two items come to mind that haven't been mentioned---Bolts that hold cam plate on may have heads that are too thick to clear the gear--- some aftermarket cam gears are wider and hit block area above the oil galley area, plug you put into galley may not be deep enough causing back of chain/gear to hit it,and also some strokers have interfernce at where the oil pump mount area is on block(counter weight hits.

also ---fuel pump eccentric????

ok maybe more than 2 but I'll only charge for two!!!!!