I've made pulleys the way others here have suggested and for a 4L or 5L pulley it's easily doable with hardly any chatter. A die for 1 1/4 tube would be a whole different animal. That's a lot of surface to use a forming tool on. I like what Tom suggested about using the mill. Anyway you look at it, your going to have to weigh the time involved vs just buying the dies you need. I tried making a die for 1 5/8 tubing a while back. I started with a cast flywheel from an old press. I hogged out the majority of the material and tried using a forming tool. The chatter was terrible. In the end it didn't work out well. Good luck with your project.
Chuck
Chuck