why not use a spandex material to cover the wood buck, then spread fiberglass resin on top of it to make the mold nearly perfect without even any sanding? then you can spread bondo, or some other body filler to get your finished shape.
I have used this method on making speaker boxes, and custom dash/consoles on 1:1 cars. it is quick, hardens in about 3 hours or less (full cure) then smear with your body filler.
the only bad part would be that you have to reduce just a little bit of thickness from your buck to maintain scale. The thickness is not an issue on 1:1, but on models, 1mm is equal to 8mm in 1/8 scale, so it could make a difference.