1995 Astra 1.4 engine rattle after head gasket change

Hi,
I have recently aquired a 1.4 astra 8v that needed a head gasket change. I have now changed the head gasket but the cam rattles like mad. All I have changed is the gaskets and it didnt rattle before at all. It now sounds like all the tappets are gonna jump out the rocker cover. The tappets are non ajustable and they sit on these shim things. Is there a particular order the tappets go in?I have two tappets with small holes in. Do they go in a particular place?
Any help would be great as I have no idea why its started rattling.