Help identify this Ruger handgun

[Sailormilan2]

That might be an AMT copy of the Ruger 22 pistol. AMT copied both the Ruger 22 cal pistol and the Ruger 22 cal rifle in stainless steel. They had barrel options of standard and target in lengths up to about 14". Heavy Target barrels to about 10", and the tapered barrels to about 14". IIRC.
Ruger sued and they had to stop production. The nice thing about them, is that the tops of the receiver tube was grooved for scope mounts.

[ar15barrels]

I thought MK II's have a push button mag release?

You are thinking of the 22/45 mark II or mark III which have a plastic grip frame.
All steel frame mark II or earlier ruger 22's will have the mag catch on the heel.