I used my bowsaw to cut the rest of the curves. BTW, this is not an easy saw to master, but I'm learning. After sawing, most cuts will be skewed a bit from front to back of the handle blank, so I square everything up with a rasp.
To cut the blade slot I use the trick with another saw, clamped upon a bit of wood, half the width of the sawhandle. This lets you cut a groove very accurately.
I finish the cut with handle clamped in the vise. It's now pretty easy with the groove allready started.
Then the next difficult bit, chopping out the mortice for the sawback. I mark it with the back in situ. Then drill a hole in the bottom and start removing wood with narrow chisels. Very carefully, slowly widening and deepening until I am happy with the fit.
And then it's time to see if everything is still straight. Luckily the groove for the blade is perfect. But the blade is bend a minimal amount below the handle. So I suppose the back isn't 100% correctly fitted yet. I'll sleep on it to see what I will do about this.