Mat,
I have the same blinker assembly w/ignition plinth that you currently have in your car, right here beside me. I removed the key housing on it and filled in the massive hole with aluminum and JB Weld, a skim of Tiger Hair, then filler and paint and it looks like the key was never there, yet retains mounting for the blinker assembly and off of the upper steering shaft supports and bearing.
http://img.photobucket.com/albums/v136/TeamEvil/smoothhead2.jpg
http://img.photobucket.com/albums/v136/TeamEvil/smoothhead1.jpg
You want?
You got, just lemme know your mailing address and I'll send if right off to you. You can swap you internals over to the new housing, re-wire the key to the dash with any key switch from everywhere from Walmarts to Pep Boys, or the internet if you must.
And you're done ! ! !
If you're leery of doing the swap over yourself, pull that out of your car and send it to me and I'll do it for you. I'll even drill some little holes in that big ol' directional shaft for you, make it look more vintage and race-ready.
Lemme know,
TC