smaller pulley will still use the normal belts yes.
and yes you can swap for a larger single belt. The usual (and best in my opinion) is a toothed belt conversion which uses a belt not too dissimilar from a cambelt, I have seen toothed belt kits on german ebay (although they possibly aren't that good) or look for PSD kits for sale second hand on here.
there is also a single ribbed belt conversion (which is what g60s are normally like), I think G-Laderseite.de sell these.