Steering wheels question??

Well... I decided to look into a new steering wheel. I figured that would be easy enough. I wanted to get a Tuff Wheel, and Grant makes one for a good price. It says for the "E-Body" so I'd need an adapter I assume?
What I didn't realize is that they come in different sizes! Is there a size that would be proper for out cars? I have a 73' Duster. They seem to have 13",14" and 15". It SEEMS like the stock one on there now is 20" lol! IDK?

I am not firm on the Tuff wheel, so if someone has a cool idea or something, let me know!

Thanks much!