P 21 = hardtop Westy
P 22 = pop top Westy
P 27 = pop top deluxe Westy

Go here and read the lists of what each model comes with:

http://www.type2.com/bartnik/csmanual.htm

Page 4, 1. basic equipment, is the P 21
Page 5, 2. pop top is the P 22
Page 5, 3. deluxe is the P 27

Look at the metal plate on the lower corner. If it is a Westfalia bench/bed, it will say Campmobile 70 on it. Then it will have one number then a period then a group of numbers. That 1st number is the year. Full width will make it a 4 or a 5 for 1974 or 1975 [in the USA].