Just popped into my head that you'll also need to check your saddle height as the cleats/pedal combo will be thicker than a standard pair of pedals meaning you'll need to raise your saddle.
Dangle your feet off the side of a table, work out what natural angle your feet sit at. Trasfer this to the cleat position. Start off with the pedal spindle level with the ball of your foot and go from there.
You can always reposition cleats with the shoes in the pedals to work out what angle the shoe would sit at.