Prior to this car I built a Hawk 289, using a 289 6-bolt motor and a Tremec T5 5 speed gearbox with overdriven top (subject of the recent 2011 Euroclassic thread on this forum). This had a 3.54 diff ratio which gave lovely driving around the twisty stuff, but with the 5th for motorway use. That is always an option, but having gone to so much trouble to install the correct engine and gearbox in the current car I'd prefer not to muck about with 5 speeds. That solution would also require some welding for the transmission mount, as the T10 (original) gearbox has very different mounts to a T5 5-spd, which I also don't want to do.
As Tim has suggested, a Cobra is not the ideal car for touring in any case. I took the Hawk to Rome, Madrid and a few other places, and whilst it's great while the sun is shining and the scenery's good, it gets very tiresome when it rains, is grey and damp, and in cities. As noted I do have a Mustang which has a 3.25 rear and 5-spd with overdrive, so maybe I'll stick to that!
Interestingly Sunbeam Tigers, which used the 260 motor, all came with a 2.88 rear (albeit a live axle). My Jensen Interceptor 7.2 (now there was a car for touring) also had a US spec 2.88 rear axle ratio.