Did you buy the "factory seat with factory base" swivel adapter (#119015) from discountvantruck.com?
Forgot to add that I am doing a campervan conversion on a 2020 NV2500 Standard Roof and a swivel seat would be a perfect solution for having more usable space. Getting rid of the "black hole" bottomless pit center console would be a good thing. (Plan to replace with something useful that has an armrest.)