It is certainly strong enough, and can be made to function with the Rigby, although you will have some work to do. Many original Rigbys were built on standard M98 actions, re: Harry Selby's rifle. You will have to open up the bolt face, and the rails. I'm not certain if you will need to open the length of the action and magazine any more or not, but you should realize that there is going to be work and expense involved in this. Have you considered using a drop box magazine and bottom metal?
That said, it should be a "class act" when completed! Best of luck with it, and please fill us in on the details if you pursue this.