Drill out the M6 holes that will locate the lateral spars which support the seat itself.
Notice firstly that you can twist these side-bars in order to drill them out that much more easily, and also because they will need to be turned through ninety degrees from the time we marked them with the bradawl.
Secondly that the lateral supports will be fixed as all else with domed M6 bolts that are fastened happily using an IKEA Allen key.
(If you've not heard of IKEA, incidentally, then you shouldn't be building helicopters).
