I’m building mine from a kit, but you could build a simple flattening jig for your router and essentially flatten your ramp. The jig is basically a U-shaped frame that your router sits/slides on. Stack the two pieces you want to scarf together with a suitable offset (ie 4″between ends), and run the router jig across the ramp. Make sure the pieces and the jig are well secured and any runout at the end cuts into a sacrificial board. I hope this is enough info for you to draw upon.