Hi Rob, nice to have you back mate. I've got a propellor clock at home here, although mine is a glass fibre casting. Quite a few years ago, a friend of mine made a number of these, finished in various colours. They were made by making a mould from an actual prop, I think from a Tipsy Nipper IIRC, then just building as normal with glass fibre matt, then finishing. If you think this might help, I can take some pics, and close - ups of the 'hollow' interior of the hub, where the clock fits.
If you want to make a real wooden prop, then it would be best to make this from laminates of an easily worked timber, perhaps even Balsa. Rememeber. it's only going to hang on a wall, not be under stress from an engine!
Glue the roughly shaped layers and, when totally hardened, trim and sand to shape. Cut and ream the hole in the centre for the clock pack - a simple battery operated quartz unit will do, available from some hardware outlets, clock makers, or even canibalised from an existing clock. This is fitted last. Stain the wood the deisred colour, seal with a grain-sealing varnish, such as sanding sealer or bannana oil, then apply around 5 to 6 coats of good quality, clear varnish. Polish when hardened, and voila! One prop clock.
EDIT: Forgot to add, if your stepfather needs a rough drawing of how to do this, let me know, and I'll either e-mail it or post it here. The work is fairly time consuming, and some needs to be accurate, when it comes to 'feathering' the laminates, but it's not too difficult.