I started a thread in 2010 about the Abergas boiler we had in our old house, some interesting input from several people who'd worked on these boilers, and particularly regarding it's efficiency for its time.
Abergas HTM boiler | DIYnot Forums
Still interested in anything anyone may have on these. Have found an article held by BSRIA, 'The boiler from outer space', but need to be a member to access it!