Want to change input shaft from 23 spline to 18 spline

So far as I know (old memory) the gears are different, IE you cannot just toss an 18 spline in there

"Not if I need to change internals to Passon OD instead of buying 833OD"

What does that even mean?? I don't think you can create an 18 spline OD if that's what you think.