Should be about as strong as the stock coupler, since the attachment mechanism (i.e., the screw) is the same. If there was one area where I would be remotely concerned, it would be where the shaft was cut down just behind the coupler, but it's just not going to be an issue. The pulling power of this loco is so far below the tensile strength of the coupler, anyway.
Before I saw this post, I also installed Kadee couplers in the Davenport. I did it two ways, both somewhat similar to methods shown in this thread.
Both ends of the loco work fine now and there are no modifications at all required to the loco proper. One reuses the stock spring and splices it to the coupler from an 835 kit, the other uses the coupler from the 820 kit.
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