Thanks all for the replies so far.
Yes that plastic thingy can be removed from the top through the surround of the finder. So I gather then that if I get a decent focusing screen I wont need the fresnel? It can go in the bin where it belongs!
I've had the lower gridded screen out to give it a clean and that wasn't too difficult so I'll probably take the advice and get an Olsen screen ... I'm not too keen on spending $200.00 at this stage. TLR shooting is still a little new to me.