multiple tapered housings were the challenge on the Russell Colbath project. Our field expedient worked well. We drew the angle of the taper on two pieces of scrap 1x stock and temporarily screwed (to each side of the timber) the ramps to the timbers so a right angle plunge from the plane of the ramps worked fine. The router had an enlarged base plate to span the stock easily. With a little trial and error setting the plunge depth for hand guided trips up and down the ramps worked fine. Cost pennies, effect priceless. Several of the crew participated. Might even be some pics on the project page (haven't looked lately)