Engine numbers

Hi cudamark thanks for the reply ive been doing some searching and found in that year that they ran the same casting numbers, but they are conflicting as some sites say different , but in one forum this guy had the same casting numbers has to i have and found he had partial engine numbers as well on his 273 and was told that was common for that year.I removed the rocker covers and checked the casting numbers and found in that year the 273 and 318 shared the same head casting numbers so the only way is to remove the cylinder head and check bore sizes.Will do that later on as at the moment im painting the underside, and after the new year getting the whole front end redone,as i have all the parts just need to get it fitted after the new year and get the girl on the road.