According to my 'Motors Auto Manual, they were all 161 either L head or F head depending on the model of the car. Larks and Falcons were L head, Ace, Wing and Eagle were F head. The 226 motor was introduced in 1954 in the Ace and Eagle models, which it says were L head motors. In 1955 the last two models were the Bermuda and the Custom 6, still L head 226.
The Jeeps and Trucks also had a 4 cylinder motor, Jeeps: 1952 4/L 1953-59 4/F, Wagon; a mixture of every combination I have already mentioned including the 6's