The sump needs to come off and the cylinder head needs to come off so you can remove the pistons and then renew the piston rings
So if you do this work you will need a new head gasket set , a set of piston rings , and new timing chains and if you go the full hog then you will renew main and big end bearings. which you might as well do if you are at the stage where you have removed the sump and cylinder head