The chinstrap and the liner look to me like they are made after the WW2. I have tried the liner in the green army M31 previously shown in this blog but it didn't give me the right look and feel for a M31 helmet from that era.
I decided to restore this helmet as a Gendarmerie / Rijkswacht helmet.
First I cleaned it and de-rusted it with HG Roest-oplosser.
I removed the lion head to get all rust removed. This picture shows there was no paint underneath the lion head and this tells me the emblem was installed before the helmet was painted.
I decided the re-install the emblem again after removing the rust and before the painting.
Next I filled the hole in the comb with filler.
The helmet got sanded and sprayed with grey primer paint.