The MK1 mag did not have what is known as an auxiliary spring attached to the front inside face of the mag but the MK1* and onwards did. These MK1 mags are rare and expensive when they do turn up and I have never seen an example in the flesh. The member who posted post 1 has since emailed me some pictures, very kindly, but I assume doesn't wish them to be made public which I will respect.
I have no problem with the pics being made public, I'm just useless with computers and can't upload them!