I got intrigued about the history of inline-6 bikes and here is what I found along with enough links to get you going:

Vintage - Size - Manufacturer/Model - Link
1957-1958 500cc MV Agusta 6-Cylinder http://en.wikipedia.org/wiki/Mv_agusta
1964 250cc Honda 3RC164 http://www.cyclechaos.com/wiki/Honda_3RC164
1965 250cc Honda RC165 http://www.cyclechaos.com/wiki/Honda_RC165
1966 250cc Honda RC166 http://www.cyclechaos.com/wiki/Honda_RC166
1972-1975 750cc Benelli 750 Sei http://en.wikipedia.org/wiki/Benelli_750_Sei
1977-1978 900cc Benelli 900 Sei as above
1978-1989 1300cc Kawasaki 1300 http://en.wikipedia.org/wiki/Kawasaki_1300
1979-1982 1047 cc Honda CBX http://en.wikipedia.org/wiki/Honda_CBX