diesel timing help!!!!!!!

hi there i have a series 3 5 brg diesel and i am putting a new timing chain on it as the old one is badly streched. some one has been in the engine in the past and put rough marks on the gears which dont make sense and dont line up with anything the engine was running but was not right and i think it may be a tooth out. how do i go about timing the gears ready for the new chain any help would be great regards sandy

it needs more accurate cam setting than marking sprockets as said in pm,sprocket has 6 key slots that are set at different positions to match chain ,sprockets to exact ep (exhaust peak)