The curve is not an issue, you end up with a shaped handle. I do flatten the back of the handle before I run the wood through my bandsaw for stability. I like to glue on wood to thicken the handle, this reinforces the splice even more.
I flatten the billet like this;
![](http://img.photobucket.com/albums/v181/ekrewson/bow%20making/limbreplacement2.jpg)
And add wood to the handle like this;
![](http://img.photobucket.com/albums/v181/ekrewson/bow%20making/limbreplacement11.jpg)
I have made over 100 bows with spliced billets, thick handles, thin handles, mostly osage ,maybe a few hickory and red oak. None have ever come apart on any poundage bow, I used urac and now use unibond.