Diosol was mainly a mixture of Tuolol, (Tuolene), and Xylol, (Xylene). I found out that Xylol was the majority of the two percentage wise. The original Scalecoat thinner was a mixture of the same two solvents as well, but with the Tuolol being the majority.
When I lived in Mobile, Al. one of our club members there was a chemical engineer. He took samples of each to his lab where he worked and analyzed them for us. IIRC, the ratio for Diosol was 55% Xylol and 45% Tulol. For Scalecoat it was 60% Tuolol and 40% Xylol. Since then I have always tried to get both solvents and mix the two for each paint I was using at the time. Its now gotten very difficult to get Tuolol around here, but Xylol is readily available.
The other ingredients were things like stabilizers and other solvents. These were often in such small amounts as to be unimportant when mixing your own.