I'm not sure it isn't still a lot bigger than you really need. The raw motor itself is 170gms or 6oz. That's a pretty fair size hunk of weight in the nose on such a lightly built model. But while it may not be a perfect match it's not too far off on a 100 inch model. Don't be surprised if it ends up forcing you to move things back in the model to avoid adding tail weight to get the right balance. And certainly at 575 watts for max power it's more than strong enough depending on your prop and pack.
With a Riser 100 my goal would be to keep it in the lower 40oz range. After all it's a design which is best used as a "floater" due to the wing section being pretty basic. And that means I'd only need a motor that can handle somewhere around 300 to 350 watts max and then run it at around 200 watts from a 3S pack to achieve 80 watts per lb. And from browsing the Hobby King range of motors that suggests that I should be able to get that much power from a 3 to 4oz motor.
And in fact I'm looking at some different Turnigy motors for a glider I've got which up to now has been using the original can motor and gear box. One that has caught my own eye is this one;
http://hobbyking.com/hobbyking/store...ner_Motor.html
I like that it's got a nice strong 5mm shaft so even if the prop folds with on blade down so it is still going to dig in that the shaft SHOULD be able to take that much dig without bending. It's got more than enough power for a lighter Riser 100 with a max power rating of 443 watts and best of all for your case it's only 105gms or 3.7oz to sit in the nose. And that means you can go with the ESC and battery pack in the nose behind the motor and go for a little more pack capacity if you need any extra nose weight. There's no information on the prop sizes either from HK or user reviews yet but with a Kv value of 1050 it suggests that props in the 11 to 12 inch range would be suitable.
To me this suggests a better option.