Bob,
The original rudders we're/are 3 piece rather than 2, but if you find wood straight, flat, and wide enough, do it with 2.
I suggest starting with 5/4 rather than 8/4. You'll save a lot of sanding! Your shaft is 1", so that's your minimum thickness, but glassing up from that will get you back to 1.25".
In the original, the first piece was screwed to the shaft top and bottom. The middle holes let bolts through to hold the second board. There are adjustment pockets in the middle of the second, probably filled. The third piece was held to the second with both drift pins and screws.
When you measure to template, don't forget that the first piece is routed out to mate to the shaft. If you overlook this, your rudder will end up too small.
Good luck, and do post pictures when you finish!
Jon Simpson
E160 Elan