Wow Dan, that really looks good, but you're going to have to stop, you're making me look bad!
I also thought of making the face out of metal, but didn't have a way to cut out the odometer opening neatly enough. The up side to doing it is you could eliminate the trip odometer and ot would make things a little easier. One tip ill give you though, if you do it, the metal will need to be really thin. If its too thick, the odometer will be too far from the face of the speedo and won't look right. When I first started trying things I tried to use the original face, but since it kind of tapers in around the odometer opening, it just didn't look right.
Keep up the good work, and later this week I should have some more progress and some more pics of the process to post.