Thanks Dayton.
This site has specs listed.
http://www.gtgtandems.com/specs/burleyspecs.html
For Rumba it says:
1998-1999: precision sealed bearings oversized rear.
2000-1: burley sealed cartridge
2002: truvativ (others have shimano, etc.) In this year, it looks that they are all generic.
So, are these bearings just like a a sealed cartridge wheel bearing? I'm now picturing bearings like these:
http://www.endurobearings.com/
that are press fit between a shell and the axel. The shell would then go into the eccentric piece that either screws or is pressed into the bike frame.
If I understand it right, the whole purpose was to have a wide (82mm) bottom bracket shell.
I have no pics, because locally means 3 hours of driving round trip. If the whole thing is going to lead to a royal pita down the road, I'll skip the trip.