Well, I seen John Pett on the 1841/51/61 CR in Sheffield, and on the first hes a groom, and on the second a gentlemans servant, and on the third a Cab Proprieter. They are living in a house, their neighbours arent giving any clues by their occupations or surnames, and there are a few other Petts living in the Spalding/Pinchbeck area, with non-romany occupations. Id have to say that it seems unlikely that this family are Romanies. I took a look at Spalls in Bruisyard Sfk, none in the CR, BUT - theres a whole generation of them on the IGI. This suggests a possibility - if the Spall family had all their kids baptised there, but none of them could accurately recall their place of birth for the census. To be honest with you, the mention of the name Green flags up more Romany likelihood than the others. Green is a known name.
I know thats not a lot of help, but Im afraid I cant see that I can find out much more for you. Sorry - perhaps someone else can.......