Looking great man! My project has stalled due to unemployment. You would think it would provide MORE time, but in reality provides less.
I would think you could make a hole in the top of your headlight bucket, put the speedo in there as far as it will go, and bondo/fiberglass a cowl up to the rim to make it somewhat seemless, then attach some mounting points inside the speedo housing to match up with the original mounts on the speedo, perhaps? Paint to match and hopefully it looks cool.