I have over a hundred pair of yew billets, and I've never spliced billets before, so I have a friend who's a cabinet maker, build me a jig.
It's a plywood sled with a fixed block of wood, that I add a spacer to and then a wedge to make the three cuts for a Z splice.
I first make sure the side of the billet that goes against the fence is relatively straight and flat (about 10"), clamp the billet so it doesn't move, and I get a perfect cut every time. You may have to fine tune the two billets for a clean line appearance at the end.
I have a photo of the underside of the sled showing the guide attached, that fits the track on my bandsaw and a stop for the length of the cut.
I hope you find this helpful, because I couldn't find a design, except for the one shown in Billet To Bows from St. Charles, that I didn't know how to build.