No point asking Clive .. he's an aerodynamicist and, hence, only talks in slugs/cubic foot.
That's because of my age not my profession - real aerodynamicists get around all that by using non-dimensional quantities like CL and Cd.
IIRC, the drawings were dimensioned in both units, but all threads etc were metric. Dude would know that better than I though. There was never any real difficulty with it.