first take the exhaust off along with the oil pan and the main stud girdle. then take one rod cap off at a time and check them. if its just a clearence problem plastigage and go up to the next size bearing. if its spun the bearing in the rod and scarred the crank then you will have to pull the motor and get a nother rod and polish crank or even weld it up an turn it back down if its run too long.in the worst case might as well rebuild all and see what caused it!