The site Lewis linked to also has a good guide (model ID tab) to narrowing down the age of your Pug by the headtube badge and decal style.
As he says it will almost certainly be 126mm, but you can happily use a 130mm wheel: the stays will happily spring the 2mm either side or you can get it cold set to making wheel removal easier.
The only thing to be aware of if using 130mm, is that the smallest sprocket doesn't foul the chainstay.