+1 on Calfee or Co-Motion.

Also Rue sports, Yin an Yang tandem would be an option. http://www.ruesports.com/frames/tandem.html

The Rue is built on 130mm spacing, which should be fine for your team weight, and gives you a lot of wheel options, such as Zipp 404 clydesdales.

As for Rim or disc brakes, I think the preference for racing tandems tends to skew toward Calipers.

At the Co-Motion Classic Tandem Race this year, my guestimate would be 10-20% of the bikes had disc brakes.

High quality calipers will stop the bike just fine. And Heat build up should not be an issue given your team weight, and since the intended use is racing, you won't typically be riding the brakes.

We did Everest Challenge on the Tandem last year with dura ace calipers and no problems.

However if you're specing a custom tandem, it wouldn't hurt to have a disc mount built into the rear drop out just inc ase you'd like to change to a disc for some occassion down the road.