Have you thought about simply modifying your TB instead? The base is thick enough right behind the throttle plate, you could bore a hole in from the firewall side. You got me out looking at my car with this post
I've also heard/read of others boring into the inlet of the SC for this same reason. Just a small hole. No biggie, really.
To have a spacer machined, buy the stock TB seal (gasket). Anyone can machine a 1" spacer with that as a model. That will effectively block off the coolant passage.