I have a swivel base I purchased off another SMB Forum member that won't work on my van without more modifications than I'm willing to do.
Handle is on the right side and the swivel mechanism seems to work fine.
I purchased this base for $70 and will sell it for the same plus buyer pays shipping. I'm in SoCal if anyone wants to arrange pick up.
Dimensions are as follows for the top and base bolt patterns:
Top holes = 9.75" front to back / 14.75" side to side
Base holes = 9 & 9.5" front to back / 10.5" side to side.