^^ aye as said sticking with a 1300 lump would make your life easier, pretty much engine out -> engine in swap. Just be aware if you fit a GT lump it may be quite spensive insurance wise due to it being in a higher group.
Plus also check you can still fit your old 1.3 fuel pump to the back of the head, MK3 Polos all have variants of the digifant fuel injection system and electric fuel pumps! I believe most polo heads should just have a blanking plate over the pump hole, but its best to check. Oh and you'll want to have the cam cover off to check the cam has the pump drive lobe on.