Damien, If I remember correctly, your car had a Moto-Lita or Grant steering wheel on! Correct? If you still have it, look at the hub, there should be a number stamped on it and find out from Moto-Lita what is the hub made for. I hope this will tell us where the steering column came from. (Providing of course that the hub was not machined)
I think the easiest thing after that is to fit a replica Cobra wheel. I will measure mine to see if it is 15" or 16". To make it look like the original, you will have to have a wood guy remove the rivets and install new wood as the 428 wheel does not have rivets. The hub will have to be machined to fit your column. FYI, Cobras had VW beetle steering columns. Your car is the later car like mine and I would love to find out where the steering column came from, maybe we can from your Moto-Lita hub![?]
Thanks,
Emmanuel