Numpads on the left hand side of the keyboard.
1st day in. Harder to get used to than I thought. I've actually caught myself moving my right hand over to the left side to the 10key--dumbass hehe. I suck at being lefty. Trying for week maybe month.
Reminds me of a time, as a young lad, I thought it would be a good idea to swap my left and right hands while riding a dirt bike... I only tried that one time 
Just moving the numpad and switching hands is really hard, because if your “muscle memory” is based on using your right hand, then you’ll expect to use your index finger for 1, 4, 7, your ring finger for 3, 6, 9, maybe your thumb for 0, your pinky for plus and enter, and so on. But now on your left hand, you suddenly need to use your ring finger for the leftmost column and your index finger for the two columns on the right, and pressing 0 is a big pain. (Question for folks who use a numpad with the left hand: how do you press 0?)
If you mirrored the numpad layout right-to-left in addition to moving it over, then I bet you’d be able to learn to type on it with your left hand relatively easily. That is:

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In general, the standard numpad and phone keypad layouts are really great for typing numbers by pecking with one finger – that’s basically what they were designed for – because they are relatively compact so your one finger doesn’t have to move all that much to reach all the numbers. However, for touch typing, they pretty much suck (in a similar way to the standard Sholes/QWERTY layout for a full keyboard, which was also basically designed for hunt-and-peck usage).