Tim, when are the pre orders available for Japfest?
I would use a 5w-40 synthetic and you will find those through the link below.
http://www.opieoils.co.uk/c-656-5w-40.aspx
Out of those, the best ones are the Silkolene Pro S, Millers CFS, Motul 300V, Redline and Gulf Competition. The Motul 8100 X-Cess, Gulf Formula G, Fuchs Supersyn and Mobil Synt S are good, cheaper alternatives.