'77 DT250MX airbox cover

I am renovating a '77 DT250MX which was one of just 450 specials supplied to the Danish army.

It has uprated front forks and an extended fuel tank as you can see from the picture.

I have been able to source most parts that I need but two items are yet to be found, namely a complete exhaust system and the side cover for the airbox which when it is available is at an astronomical price due probably to their scarcity. So I have decided to try and make one.

I have the air filter end cover which is held onto the airbox with 3 screws but what I need is a clear picture showing how the outer cover is attached  to this inner cover. It looks as if it was with some sort of rubber hinge but I would like to have details of this. So if anyone can take pictures and either post or send to me direct it would be greatly appreciated.

Here is a picture of my bike as is and another of how I hope it will look when finished