Right now we're looking at using a rivet. The reason being, is that the RCMP have suggested either this or a physical dint in the mag body. The RCMP have cited case law on these methods as being "permanent", so according to law in Canada, a rivet is a permanent blocking mechanism. Any internal blocking mechanisms are NOT. If you don't like the rivet, I would suggest looking at the 10 round size mag.
Also, as a side note, because the AIA Enfield magazine has been officially identified by the RCMP as a dual use magazine with the M14 rifle, I'll come right out and say this: Yes, the mags are designed from scratch as AIA Enfield mags (different rear lock up tab dimensions and no hole in the front of the mag - for starters), but they still work in a M14.