And of course, I have neither in the building to look at right now.
If I recall though, the factory 702 mag (good guess, eh?) has it's baseplate held in place by a roll in the mag body itself, like a savage 64 mag. That said, the smarter way to do this is to probably flair the bottom of the body (if you can do this - there's a fine line between enough flair and effectively breaking the thing or now having a 9 round mag) , oversize your new plate, then fold and pinch the edges on. for good measure, divot the front and back.
It should stay on just fine. They aren't exactly high quality mags and the spring pressure is pretty low. All that said, fixing mags is something myself and the other people here never touch, as it's usually more fucking around than it's worth. So take that how you want.
Alternatively, you could use some of your handy sheet metal to make a less-trash feeling 715T out of the gun. That would be lulz.