Funny that this should show up. Disclaimer: I am NOT a mechanic by any stretch of the imagination.
A couple of years ago, I had a 1979 Johnson 25 that had overheated with the previous owner.
After removing the heads, I saw that the "rubber things" in the water jacket had hardened and
were crumbling from age and the overheat. With the help of "Pappy" here, I was able to replace them.
First attempt I used the OMC replacement that was solid rubber and had a slight taper. This did not work
AT ALL – – – chunked those, bought another set that resembled the rubber hose and they worked just fine.
easy to install with a little gasket cement for lube and all went well.
So from personal experience, I do not suggest the solid rubber with a taper unless your motor specifically calls for it.