How do you propose to hold the gun?
For a ghost ring to work, it must be close to the eye - less easy to acquire as the distance from the eye increases.
Depends on the ghost ring. There's lots of pistol ghosts and in fact, they actually make ring sights specifically designed to mount on the barrel of rifles

But I really won't know till i see the thing and shoot it. However many of the mare's legs i see being shot in various vids are held not much farther away from the face than a pistol might be, so it seemed like one possibility. I have a side mounted sight here, i thought i'd just 'duct tape' mount it so to speak to see how it looked to the eye.
Just one of the possibilities. Hell - i might even mount a mini red dot on it and go for the 'firefly' look
Most likely tho i'll just replace the front blade with a fibre optic and replace the rear ladder sight with a fibre optice version that's more adjustable (like the Hi Viz version), to get a little better accuracy and low light performance. If i get good enough with the thing to take it hunting or to use it as a camp defense gun, i'll want a little better low light performance
I am curious about the grip and mounting position of this rifle... I was thinking to hold it with my arms extended and elbows slightly bent and positioned outward; weak hand on fore stock and strong hand in the usual position. Are you planning to mount it more like a rifle and pull the stock in closer to your shoulder? Maybe with the strong side elbow tucked into your chest?
well - one shooting 'expert' who shot an almost identical gun and did a review on it suggested he got the best results from a 'push-pull' grip with the gun in front of him much like a pistol. He claimed he was able to get very good accuracy. Check out this vid:
http://www.thefirearmblog.com/blog/2009/09/02/jb-custom-mares-leg-pistol-video-review/
Now - i take such reviews with a grain of salt but several youtube vids of guys shooting theirs seem to suggest this stance is popular.
Again - only way to really know is once we've got 'em and we can play with 'em.