Hi Dan:
I was talking to an insurance agent here in Texas a few months ago. He is building an -8. I believe he had the empennage done and was working on the wings or fuse (can't remember which). He registered his airplane (you can do this if you have Van send you the final paperwork, you don't need to have the airworthiness certificate).
He got a tax bill from the Great State of Texas saying they valued his airplane at $100,000. The tax bill was for about $12,500. Needless to say he was not happy. I haven't followed up with him after giving him some suggestions on how to handle the situation, so I need to do that. But the point is, apparently Texas looks at the FAA registry and checks it against tax records.
So you might want to wait till you're close to being finished before registering. Oh, and put some tax money on lay-away.
Chris