Not sure of width, but they look quite slim... and personally I would re-cover the central bit!
http://cgi.ebay.co.uk/Lotus-Elan-M100-seats-Also-suit-Kit-Car-etc-NO-RESERVE_W0QQitemZ190123359763QQihZ009QQcategoryZ27375QQrdZ1QQcmdZViewItem#ebaypho
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