Dear Luigi,

Not knowing the luthier and in view of the lack of an adjustable truss rod in your instrument, I might suggest you start with the lower range of gauges I suggested, i.e. .012 .024 .036 and .048. These should certainly be comfortable for you and the instrument at the scale length you mentioned. If you find that the instrument could be "driven" more (my current Terry Docherty octave mandola can, as could a John Le Voi model I used to have way back but not the Paul Hathway model I had which was more lightly built and so was better with the lighter strings) you could move to the heavier gauges. The gauges will also work fine for GDAD but if you permanently go to GDGC you could use a gauge higher for the top two pairs.

Peace

moo