I second the 195 thermo - I tried the 180 one in Geronimo, then put in the 195 - world of difference.Stock thermo in 1980 in the US was the 180 - the 195 was the canadian stat. NGK plugs are indeed reverse of other plugs - each number is 1/2 step of a heat range - other plugs are a full step. I have run Geronimo at 10btdc for years, but my truck also has a weber carb, header and custom flowmaster exhaust, so he is not stock.