Definitely not as simple as that.
1. Aircraft.cfg - imperial. Weights in lbs, speeds in knots, measurements in feet. Fuel capacities in US gallons, engine boost pressures in inches of mercury.
2. airfile - imperial. Weights in lbs, speeds in knots, measurements in feet.
3. Allied bombs - metric. Case in point, the stock a_500lb bomb, Mass="226.8".
3. Axis bombs - metric. Case in point, the stock g_sc500 bomb, Mass="500".
4. Null pylons - metric. Everything in guns, pylons and weapons is metric.