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_agusta1964 250cc Honda 3RC164
http://www.cyclechaos.com/wiki/Honda_3RC1641965 250cc Honda RC165
http://www.cyclechaos.com/wiki/Honda_RC1651966 250cc Honda RC166
http://www.cyclechaos.com/wiki/Honda_RC1661972-1975 750cc Benelli 750 Sei
http://en.wikipedia.org/wiki/Benelli_750_Sei1977-1978 900cc Benelli 900 Sei as above
1978-1989 1300cc Kawasaki 1300
http://en.wikipedia.org/wiki/Kawasaki_13001979-1982 1047 cc Honda CBX
http://en.wikipedia.org/wiki/Honda_CBX