Its a custom 18 bikes frame with paragon sliders for a rohloff, bought at a bargain price off of ebay as size wise its pretty much perfect for us. You dont find many 29er mtb tandem frames around in the right size and even rarer a custom frame for a rohloff too (been running ours for 10 years on tandem now), had to buy it and build from what we had (though not a lot moved between the two). I’ll take some extra pictures for you and post them tomorrow.
Sorry to Alex at mtb tandems as I’d been mulling over a new Fandango for a long time and his 29ers are really good too (rented one for a week which we rode at Tahoe and in Bend) but this was too good to pass up. However he’s now refreshed the Fandango again with more clearance for 650b plus now but this build has turned out as good as I ever wanted (though not ridden it yet).