That is a really-big scope for the Mini platform...probably too big, meaning that in order to have any hope relative to being able to obtain a proper cheek weld, you're either going to need a different stock, or attach some sort of added gizmo to the existing stock in order to raise it's comb-height.
As far as "what height mounts?"....other than saying that you're going to need the mount/ring package to sit about as high as you can get it, the exact answer will depend on whether your particular Mini came equipped with the "Ruger Rail", and/or which style of mounts you plan to use regardless. Plus, there aint no industry standard relative to the height of one brand's "high mount" compared to another, so then there's that.
All in all, your best bet might be to try and get some input from the scope manufacturer, or perhaps from Ruger. Other than that, about all you can do is determine how far up your new scope will have to sit in order for it to clear the rifle, do some careful measuring from the bottom of the tube to the top of receiver (or rail) where you want the mounts to sit, and then go from there.
I hope something here helped, and good luck on your endeavors.
DGW