Hatch -Match

Good afternoon fellow garage mongers! I'm slowly working my way into the dreaded "hatch zone",and have had a stare-down with these ribs I've cut out,such as they are
Now I'm going to reveal my geometery ineptness. Before I cut these wrong,and have to start drinking heavily, what is the best way to scribe the proper angle on the top of these ribs for the right cut to match the last spar between the hinge and the hatch. Does that make sense? Anyway, any help would be appricieated.........Thanks guys and gals
