Hi Gira Gira,
I got the profile for the wishbones from https://grabcad.com/library/wishbone-boom-design-for-classic-day-sailing-boat-1 (the measurements can be seen in Wishbone1png), and then adjusted the size to suit my masts and sails, plus a bit of leeway. I definitely didn't want to end up with the wishbones being too short...
Whilst the CAD drawings are for a single-piece boom, I made mine so that they could be opened at the aft end. There's enough flex in the booms that I can open the aft end to slip it around the mast, and then secure the boom on that side with a bolt through the connector piece that is glued onto the other half of the pair. I chose to open the aft end as it was closer to being a straight section of the boom, so there wasn't much sideways force through the laminates.
The contrast between Western Red Cedar and Tassie Oak would look great. I've found that Tassie Oak can spring back quite a bit, even when laminated (my rubrails are Tassie Oak, and whilst I managed with just two laminations it would probably have been better to make them in three laminates. So, thinner laminates for the boom would probably be a good idea, as would leaving it in the jig for a few days to let the epoxy completely cure, particularly now that it's getting colder here in Australia...
Cheers, Peter