Sorry it took so long to get back to this topic.
Dave has pretty much explained what needs to happen. Just make sure you use some type of mold to mold release.
Here are some pics of how one of my molds looks for a wheel. I had to make a two piece mold to cast this wheel. I wanted the same features you are looking for in this wheel. I don't have any pics of the mold making process but with Daves explanation and these pics, you should be able to see what needs to be done.
This is the two mold halves. You can see the pour hole and the area where the resin flows.

Here you can see the two halves placed together. The large hole is the pour hole, the smaller hole allows the mold to breathe as it fills with resin.

Resin poured, cured

Two halves seperated. You can see where the resin cured in the pour hole and you can also see the wheel that was created.


Trimmed wheel ready to prep for paint

Jake