I'll be anxious to see some additional, close-ups of the frame details.

While you can see the Calfee influence in the building techniques and a few features, Brent seemsto use a completely different approach for the rear triangle... integrating what appears to be a somewhat oversized pre-fabricated production rear triangle instead of stick-building and beefing up single bike stays as Calfee does. Brent's larger diameter rear stays look more proportional to the frame.

I also like Brent's approach for incorporating the integrated headset into a very lean-looking head tube which also makes me wonder if the head tube is a pre-fabricated unit vs. the 'fatter' hand-wrapped head tube used by Calfee. In fact, as I look at the frame it appears Brent simply uses a bit less material at all of the tube junctions.

The main tubes look to be sourced from a common supplier as well, at least based on photos of more recently produced nude Calfees.

The graphics and paint definitely have a single race-bike look consistent with current trends vs. the more ubiquitous solid color or fades found on most tandems.

Finally, in looking at earlier RueSports tandems I tend to get the impression Brent was the one who adopted the larger, aluminum-sleeved eccentric shell to accommodate the Bushnell eccentric which Calfee has since adopted.

Again, I'll be anxious to see the final build as it should be very distinctive given some of your component details, e.g., white brake hoods to pick up on the white paint, etc.