Well, if I were you I would put the kit on the GT. In the long run, the GT would be able to handle the additional stresses.
The GT also has disk brakes...hydraulic from the looks of it.
I can't tell from the picture if the GT's rear dropout has holes to carry a bicycle rack for the battery. If it does then you could use a seat collar that has holes for the bicycle rack to attach to it. If not, then you could always hang it off the top tube.
If you're going to order a kit off the internet then go with the Papamotor kit
. They have excellent service and several members here have their hub motors and Ping battery setup.
Both your bikes have dirt tires. If you ride your bikes on the street then you'll want to switch your tires as well for better performance.
I could continue for several pages but have a look at the Papamotor thread first: http://www.bikeforums.net/showthread...onversion-kits
There are also members with other kits. Have a look at their threads and ask us questions. We'll help you find the right kit.
The GT picture has what looks like stairs. If you lift your bike up and down stairs remember you're going to have a lot more weight to carry with an e-bike kit.
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