From another thread I can assume you'll need JIS square taper since you've decided to go with some custom-length daVinci cranks; Yes?

Phil Wood, always a good call when you need a JIS square taper: wide range of axle lengths, off-set axle options, 5mm of off-set adjustability using two adjustable cups instead of a fixing cup & adjustable cup, and different spindle options. Down side is, they're not really sealed so if you ride in the wet a lot you could end up with long-term durability issues and you need to buy a special set of splined cup installation tools.

Shimano's UN72's were my favorite, but the UN73 has turned out to be a really great option too. A LOT less expensive than a Phil in 4 axles lengths for 68mm wide BB's. This is what we use on our off-road tandem. I think Jensen sells them for under $20/ea. UN54's are OK, also cheap but a bit portly.

SKF... Everyone seems pretty happy with them. I haven't had an occasion to use them, as our Phil Wood & Shimano UN72/73s have been doing just fine. You are correct in that you could install them "backwards" to put the roller bearings on the left side of the tandem by flipping your eccentric so long as you use Blue 242 or Red 271 Loctite (apply heat to remove) on the cups to keep procession from causing them to back-out. For any doubters, this is the easiest way to make sure Italian BB's don't unscrew themselves, noting my '98 Calfee Tetra Pro single has an Italian-threaded BB: been there done that. Anyway, not sure there's a more durable BB on the market than the SKF, but they're 1/3 heavier than Phil Wood BB's (if that matters to you, ~300 gr vs. ~200). Our friend Alex is an SKF dealer: http://www.mtbtandems.com/SKF.htm

As already noted by brother jnbrown, running a spindle that is a different width or even at a different off-set than the rear on a tandem's sync drive is no big deal. I've been running 108's up front with 111's and 113's in the back for over 10 years on three different tandems. The length of the drive chain nulls out any offset issues with a chain... not so with a belt drive.

Finally, who the heck is Steve Bushnell? I think you mean Dennis Bushnell... currently the master framebuilder for R&E Cycles. Dennis came up with his expanding eccentric design back in the 90's and got around to patenting it in 2007/2008. By then, he'd had some help in refining the design from Todd Shusterman at daVinci designs, who doesn't typically get credited for his work on the refined version.

That said, Mel Kornbluh at Tandems East has come up with a modification to Cannondale's newer eccentric that makes them a pretty good choice as well. Cannondale almost got it right with their latest eccentic, but went cheap on a critical part. Mel had his machinist come up with a replacement part that solves the problem. Just something to consider. I've stuck with the Bushnell for our Calfee as I've been a Bushnell fan for a long, long time (since '98) and have them on all of our tandems.