Saw this on e-bay 
http://cgi.ebay.co.uk:80/ws/eBayISAPI.dll?...ME:B:SS:GB:1123 
Says that the 240 & 320 are the same barrel but bored out, is this correct ? 
Are the heads completely different or modified to suit ? 
Also how many rings does a 320 (280) piston have ? 
Thanks in advance 
Ross