Do you mean having the Wharram "Wingsail" on a biplan 860? I am not sure if there will be any advantage for this. Bernd would be much better to answer this. Initially I was thinking of having junk rig but Bernd advise me against it and he offered 3 options: a boom-less sail with a rotating mast so you can roll the sail around the mast for reefing which was very tempting but I was a bit nervous about the mechanical strength over time for the rotating mast, a more "standard" sail and boom combination and the one I selected which is the wishbone. The wishbone has been used on quite a number of boats and has a strong reputation for being easy to handle. There is a bit of cost for the rail and carts. Beside this is looks quite economical to build.
Sourcing the plywood could be one of the main issue in Thailand. Meranti is everywhere but not suitable and Oukoume seems almost chimeric.
Alain Dupuis