I really don’t know what the taper is. Brent had one for splicing lams for his Sheepeaters, I copied it, made mine around 2007/8. The joints are a lot stronger then the 30* ones I used before and often you can’t tell they are there.
How I made the butt splice sled. I used double sided tape to hold a 1/2”-3/4” ( +/-) piece of riser wood that was laying around my shop to a piece of maple that was left over from making my lam and taper sleds. Ran it through the cabinet saw both top and bottom to cut all the way through. Then ran it through my home made drum sander with the piece of wood still attached. Took a total of 5 minutes to make.