As i get older my sight gets worse !  i now have trouble with iron sights .  I have had this red dot mount designed and 3d printed and have had it on my Old Army for a while with great success . it may upset the purists but it enables me  carry on using it !
 
This advert is for the mount only  NOT the sight shown this is for ilustration only .
 which is a Vortex viper red dot . the mount is the 4 pin pattern and will suit many makes of sight but not all .
To fit you need to remove the adjustable rear sight on your old army . one screw and drift out the tnin pin at the front . 
Using the elevation screw from your  std sight loosely screw the mount on .  checking the hole lines up tap the thin locating pin back through the front . once in gently tighten the elevation screw  to hold it firm .  the sight sits down on the 4 pins and is held in place by 2 4mm allen screws provided . 
 sights that will fit this mount  below 

Docter/Noblex mounting standard

This is one of the most widely used mounting standards in the field of red dot sights. It has two holes for screws and four sockets in which the pins on the mount/adapter fit, one in each corner. There is a wide range of mounts for this mounting standard on the market, which is one of the main reasons why it is used by so many manufacturers. Docter/Noblex standard is simple and reliable.

Red dot sights that share this mounting standard: