If you have annealed your cases, or have new ones in 17 FB, you can just lube the case neck and slowly run the 17FB directly into your 20 VT sizing die and it will expand the neck to 20 cal.
This is what and how I do some, if I am sizing 17FB into 20vt or 20scc.
Keep it simple. Then load and fireform into your VT chamber.