Nice start on your project Beekster, I can't wait to see more pictures as it progresses. Do you make the gears and shafts as well? Is the winch frame made of sheet plastic? Just curious as I would like to tackle a similar project albeit a bigger machine one day.
The gears are standard items from Plastruct, and everything else is Evergreen stock. The bedplates are laminated from several sheets of .030" stock, and the axle shafts and winch cores are built up from Plastruct tubing. The winch flanges are slightly out of round, because the fit of the sleeved tubing isn't as tight as one might like. But it's not noticeable at all at this stage, and certainly won't be once the rest of the thing is built out and there's line on the winch drums.
The bedplates were scaled from a pile of measurements that I took of #70097 sitting in Tillamook, OR. I had a CAD-drafter buddy of mine draw up a template, and I used Elmer's glue to glue paper copies to the plastic sheet before cutting out the parts. Then it was a matter of using my True Sander to square things up and work down to the finished dimension, using a digital caliper to measure frequently along the way.
The spar is made from .500" tubing; it should be .518" in scale but I'll live with the discrepancy. Laminating a sheet of .010" sheet to the tube is damn near impossible (I tried on an earlier spar attempt), and milling it to a consistent diameter would be a trial as well. It's nearly 13 inches long!