Mike,
Check out this thread.. I took some pics and did a comparison between REW, RE, and 20B.
http://rotarycarclub.com/showthread.php?t=14
My goal of an adapter is to use stock set up such as oil filler neck, coil location (which isn't an issue for you), Throttle cable, wiring, greddy elbow, min. IC modification, etc.
Also, with the adapter, I could easily go from RE to 20B as they share VERY similar specs.