The simple method would have been to shove the split pin straight into the float's tube and go fishing. I tried that, but it stuck out about an inch looked a bit like a tangle magnet.
First cut off the top of the tube with a hacksaw. Then run a sharp blade around the bottom of the float where the tube comes out to stop the paint pulling away when you grip the tube with pliers and pull it out. The split pin is opened up wide so that it grips when pushed into the float. Apply glue to the split pin (epoxy for a long lasting job, or superglue if you're in a hurry) and push the pin home.
For a neat job, and to stop the swivel getting wedged out of line, slide a short length of shrink tube or silicone tube over the swivel and split pin eye. That's it!
When I'm in less of a hurry I use the split pin and swivel construction on floats shaped from lengths of balsa dowel. Starting from scratch with balsa means you can make the floats just the right size to suit your needs, but they take longer to make with all the shaping, sealing and painting.
I prefer this stumpy profile for my bottom end floats as I find they both hold up better in a flow, and are more visible in any conditions, than the usually recommended pencil float for legering deadbaits. They work for paternostering, too, making them an all purpose drain float.
