Without digging out the data sheets, but I think the 2708 is quite different programming algorithm than the 2716 onwards. This means that if the Dataman will really suport the 2708 then the adapter must just be a three rail PSU and transistor drivers, possibly quite easy to make.
There is a real reason why all the EPROM programmers you find start with the 2716, the earlier ones, 2708, 1702 etc are really different.