has anyone done it yet?
Is it too big problem to attach it on the left side? (because of reloading, ofc)
what kind of rail is needed?
Any kind of help is appreciated
thank you 
I had a go at turning the mount through 180 degrees, and mounting a pencil scope on there. It is quite far over to the left, could do with coming back in a bit.
you used normal (aka modern) mount?
PS. where did you get the pencil scope, I used to look for them but never found anything?
Do you know the magnification by any chance?
If you've got the ACM M14, I'd just use the rail that it came with. At least you'll be able to mount a variety of scopes.
If you do that, the rail is in the position of the M14, the M1 garand had an offset mount so that you can still insert the clip (M1 was top loading remember, M14 was bottom loaded from a mag)
