For helmet, use:
{"pilot_L39_helmet", 0 ,"pilot_L39_helmet",false};
For tanks, you need to name the material "L39_Drop_Tanks" instead of "Fuel_Tanks_L39"
However, this seems to be working only for diffuse. If you try to add specular or normal maps via description, it'll not work at all. I'm going to investigate this futher and then submit a bug report.
If there are no English labels in the paintkit, you need to create them from scratch or somehow make use of those used on Diamond textures.