I did it the other way, were the sleave pressed into the flathead throw out bearing hub and slides on the trans collar. I used cold rolled bar stock and measured the bore of the stock throw out bearing.
It was on a T5 but pretty much the same thing you are doing
I used a piece of schedule 80 pipe. Had machinist bore inside so it slid easily over the input shaft "nose", and the outside so the throwout bearing would slide easily. Tapped for a set screw toward the rear to hold it in place. Five years, several thousand miles, still there. Rod