Mark I, II .22 short bolt?

I just saw an ad for a MK series with an additional bolt for shooting shorts. I understand the concept and like the idea. (got my hack job gunsmith juices flowing...)

My question is was this a factory option?

Did a little search. Is this my answer?

http://www.gunbroker.com/Auction/ViewItem.aspx?Item=218462476

not 'factory' but as you "see" in that ad, aftermarket...OR you can take a bolt, 'skeletonize' it and reduce the spring to work for shorts, and you have to 'modify' any magazine to use the .22 short cartridges...its been done before................
so if you find a gun, thats already 'done" ( and it works) easier and cheaper, to make it back inot the 22 long rifle version....depends on the "price" as it is, do not want to reach that point of deminishing returns.........