I would not use the 1.7 unless you are able to change the dimesions of the keg box.
A 1.7 compressor is designed to cool that amount of space and the door being opened and closed a certain amout of times per day.
The plan calls for a 2.7, which will work because the space is not designed to be opened as much as a normal refrigerator is.
I built a keg box a little bigger than the plan, so that I could store canned and bottled beer, and soda in it as well.
When I did the calculations, I was much better off removing the compressor from a 10 cf fridge and installing that in my keg box.
I would guess that if you did use a 1.7 with the keg box dimesions on this site, that the compressor will be running almost constantly.