Can't agree with you more. If I need any more mags for my soon to be Winnie 490, I will be grinding off some metal too. But at under $20 US funds, the originals are not too expensive. here the stock Mark II mags are almost $30. Plus shipping if you do not live in the 'Peg.I had a choice of a Winnie 490 and a 10/22 and I chose the one I really wanted.
Out of curiousity, lone-wolf....did you have to grind off all the flange or just a bit? So if there is some left, they can still be used in the stock Mark IIs.