I was fortunate to get an un-built version of this old kit from Arnold. What I like so much about this kit is how ahead of its time it was (and is!)!
The above and below photos show the various pieces that come with the kit. Essentially the system revolves around the clear plastic boxes,and the various fascia you would glue to these 'boxes'.
The included instruction sheet provides some ideas of what a finished model could look like:
On the reverse side is a more detailed breakdown of various combinations.
The below scans from the 1968 (really!? That long ago!?) Arnold catalog and illustrates the different options of the 0679 Universal Building Kit. Note that the copy in the catalog acknowledges that it took nine (9!) kits to make the model shown on the page below!
While the below page from the same catalog isn't specifically about the 0679 Universal Kit, it does show the very 'modular' thinking at Arnold at the time. Some interesting models were clearly created from similar components as the 'Universal Kit'. Not sure of the architectural style that these would fit into....I think we all can definitely recognize the style as that proto-futuristic mod-style from the '50's and '60's (which I find quite interesting in retrospect!)
The bottom line? What a cool idea! Greenmax has certainly been the only modern attempt at something 'modular' that can be customized by each builder (I'm ignoring the transition era brick DPM modulars on purpose), which is too bad since I think modern/retro-modern architecture really lends itself to this modular component style. I for one would be happy to see the 'new' Arnold (under Hornby ownership) release these kits again!