Your dead right they were so ahead of their time, Mac Ossa monocoque frame conversion, built by MacDonald Auto Cycles in Cheshire, Dave Murray rode the first production bike in the Northern Experts. Of rivetted aluminum welded round the steering head, the bike weighed only 185 lb dry. They also made one with the Mickmar 250cc motor..
There are some photos of both trialsbikes on my website, link below.
http://www.custgp.com/trialsbiketwo.html
Cheers Will