Figured I'd put this out there as well... there's a 1990 econoline
in the Pick n Pull north of Seattle (Lynwood) with a total of four swivel seat bases in it (2 up front, 2 second row). They're all in good, functioning condition.
I have some measurements for bolt holes if that helps - I used a similar swivel base from a '90s Dodge conversion van for my front passenger seat swivel base. Believe the yard charges around $25 for the swivel base... all I had to do was drill a few different holes to have them line up with my van's base & seat. Super cheap alternative to the made-to-fit swivels. I'd offer to pick them up for somebody, but shipping would likely be cost prohibitive.