The steering wheel sits on a taper, no splines. Nut could be loose.
On the bottom, unclip the bail, then the housing needs a twist, about 1/4" to pull off.
I forget which direction, but you can see a raised bump on the can that shows how it works. Then, the 2 prong fork gets pushed up towards the wheel and a C clip will appear, bump that clip out and the horn rod will pull straight out. Lucky for you to have a rag top because in a closed car the ceiling is not high enough to get the rod out, you must drop the steering box. Be careful not to bend the rod! Also, when pushing on the fork thingy, the whole rod will want to move up. So, have some one hold the horn /light button down at the wheel, or with a yard stick or similar flexible thing woven thru the steering wheel you can do it alone