Sorry, but it was all about the 3rd original design of a carbon composite monocoque neither about the 3rd team or the 3rd monocoque. Nothing was special about the T91 since it followed closely the T87 pattern.
The Lotus T91 use exactly the same manufacturing princips than that of the T87, T88 and T88B. The T86 "Torre Canyon" was arguably different but was never raced and only the outer chassis was made in carbon composites the main body being a T81 aluminium monocoque.
The Ensign N181 was an unique piece of enginering at the time and
not built after the McLaren or the Lotus pattern. The top monocoque was carbon fiber and the bottom was honeycomb aluminium. It was sometime referred as semi carbon-monocoque.
There's no pictures of a "naked" N181 or from it's close derivate the Theodore N183 even on F1devianart. But the N181 original construction pattern which is totally different from the one initiated by Mc Laren and Lotus was re-used for the Theodore T83 Indy car. Later on, CART made this type of top half-carbon, half-alumimium monocoque mandatory for safety concern before allowing full carbon survial cell like in F-1.
Here some pictures of that car :
http://www.flickr.com/photos/31390582@N07/4173003024
You can see clearly how it was made.
Source : Inspired to Design, Nigel Bennett.
