I'll go and measure my inserts tomorrow. I have the original side pieces, but my centre-piece was replaced by a modified one, but I can get rough dimensions from that.
Kind regards,
Serge
EDIT:
I've added a new JPG with my measurements. I didn't have much time so I couldn't get everything, but I hope it's helpfull. Also, take the measurements with a grain of salt, it's the best I could do with a tape-measure and a 47 year-old piece of aluminium.