I used a Mk 2 Polo radiator, and it fitted vertically quite nicely. Managed to plumb it up using the original Sierra hoses, and some bits of metal pipe.
I have attached a link to the one I bought below.
http://cgi.ebay.co.uk/VOLKSWAGEN-POL...item5d287995b8
Price was quite resonable I thought for a brand new rad.
I have also attached a pic to show you what it looked like fitted.
Cheers
Gus