OK, what I see is. It shouldn't be hard to do a little cutting on my M1A mags. Since, I have traded my M1A for the AR10. Seems like it is ment to be.
Instead of doing some crazy measuring. Trim the tab on the back of the mag. Take out the mag catch. Insert mew mag. Use a scribe to transfer area to be cut. Check position of actual mag. Should be ok. Bolt hold open. If I figure out a solution. I will post it.
Will have to wait till I have free time. Being an adult sucks sometimes.