David Stinton, the fellow who inherited the combolins from Roy & did the recording had often done repair work on them when the Corries were performing. For those who seriously want to know what combolins are;
these instruments were designed as a pair. As stated earlier the intent Originally was to cut down on the # of instruments Corries had to tote.

The one Ronnie performed with was basically a guitar with added base strings & a mandolin added as well. Roys had a guitar using an open tuning, had sympathetic resonating strings & also a banduria finger board. ( I don't know what a banduria is but that's what the liner notes say.)
In my opinion these instruments really shine while pefroming airs.
Hope this helps, Charcloth