Thanks for that - there's always good advice here...
I've already been to my local agri merchant, and he's photocopied the Lely wheel page for me - if it's a Gemini, the wheels would be 4.00 - 8 x 4. I've sent Lely a picture and await response! I thought of doing that only after posting here of course. Does it matter if the tines are wrong? It seemed to turn the hay OK last year but rowing up was not good, with lots of hay left lying about (I spent several hours hand raking the loose stuff into the rows!). I have no idea how fast the thing should be running to make it work as it should.
Cheers,
Dave