Richard Roake (Retired Geek) suggested Eppler E836 scaled to 12% thickness ratio to me a while ago.

Target a chord around 150mm (anything smaller is to hard to build.

Span wise what did Phil recommend? Don't go any less exposed area than his original design.

0.175 sq.m (Klaus's Number) sounds about right for area so if you were 150mm that would give you an exposed length of 1166mm and a board length around 1700.

Hunt around and see if you can find someone upgrading their F18 foils.