I have a Simmons Pro Hunter 4x32 pistol scope on a K31 mounted where the rear sight was. I got the pistol scope because I wanted 4x power and it was less expensive than dedicated scout scopes.
The problem I have with a pistol scope used like this is the eye relief is still too long at 12". And that 12" is a minimum, the eye relief range is 12" to about 24", so that 12" is on the fringe of scope usability.
In actual use on my K31, you have to move your head back on the stock to get a full view through the scope. You can put your head in the normal position and still use the scope, but you get vignetting of your field of view.
To me, it comes down to how much money you can spend. If you don't have much money as many mil-surp shooters do (like me) a pistol scope will work, but is not ideal. If you do have the extra money or are willing to save some, get a purpose built scout scope with the proper eye relief range for that "instant" scope picture when shouldering your rifle.
Well after I bought my Simmons Pro Hunter,
Weaver has come out with a lower priced scope in 4x. Even though the field of view is less than that of a 2.5x, I would recommend it in a heart beat over a pistol scope now that I know better.