Just picked up a 318 with 481 hours (supposedly). I see according to TractorData there are 2 different engines. Onan B43G from 1983 to 1986, and Onan P218 from 1987 on. P218 starts at S/N 1420001. My S/N is M00318X1:14286. Never seen a Deere S/N like this. Trying to figure out what plugs...