it was addressed,and other not so favored items were added on the MARKIII pistol. it has the magazine release like an later designed auto pistol,a proper button magazine release,that you can depress with your thumb,not a europeon heel release,that requires two hands. that they also did a few other add ons like a loaded chamber indicator and a magazine safety (it will NOT fire without a magazine in the well,and will cause you to have a live round in the chamber and not able to fire it,if your so endangered and NEED that last round to fire)...hope that helps,get the MARKII. trust me,the button release will not help you that much,to be faster.
Magazine
There are a couple available for the Ruger Mark II The Volquartsen Extended Magazine Release: http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=590435 Ranch Products: http://www.rimfiresports.com/merchant.mv?Screen=PROD&Store_Code=RSC&Product_Code=RP2MR
Best left to a gunsmith
No such Ruger ever made
its thumb mark meaning one print your thumb on soemthing and itl be caled a thumb mark or some one made a thumb mark that or surch thumb mark on google images.
Primarily in the magazines; Mark II has a bolt hol open also
Go to Ruger's web site to find out.
Ruger's web site has sn tables.
Ruger's website has extensive sn data. But the Mark III started in 2004, and is still be produced.
Just bought a Ruger Mark II .257 Roberts paid $549.00
Ruger has sn data on their web site.
Unknown caliber. Contact Ruger