Your block and head casting numbers match my 1956 thriftmaster 235. It is rated at 140 gross horsepower. 128 net horsepower according the spec. plate in my door frame. However, your casting date, K2255 is different from mine. K2255 translates to the to cast date November 22, 1955 (K=11th month= November, 22 is the day of the month. 55 is the year).
