Yes M1A / M14 mags can be used in the AR-10.
Infact, they are the mags that are used, but they have to be converted before use.
You can do it at home or a better choice would be to send them to ArmaLite and have them convert them. They charge $25.00 per mag and the conversion is guaranteed.
If you choose to do them at home just closely copy the mag release hole on the side of the mag and you'll have to cut back the feed lips also. If you want the bolt to stay open on the last shot, you'll have to cut a notch in the back of the mag for the plunger of the ArmaLite follower to fit through.
TS