I suggest you don't need this "helm" tool at all. It's quite simple - a helmet is made of 2 texture files, with names like:
driver5_1.tex
driver5_2.tex
or
driver19_1.tex
driver19_2.tex
These 2 textures files are added to the cars.wad (inside the 'cars' folder).
All 22 drivers share the same shape (it is a limitation of GP4). The shape files are:
car_helmet_00.gp4
car_helmet_01.gp4
car_helmet_02.gp4
car_helmet_03.gp4
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Intel NUC 8i3, 8GB RAM, MS Sidewinder Wheel