A D80 is a big (very strong) diff ! A d70, also big but like Bill says very similar in size to a 60. You can fit the 70 gears into the 60 to save a bit more space, but the 70 has bigger steering C's and knuckles anyway. The 'optimum' rear axle i have to say is a 14 bolt, with a shave on it i've got the same clearance as a LR diff - but can now handle 500hp. These can be made into front axles as well if you so wish and are prepared to do the work.
I seem to be have been collecting an assortment of axles over the past year (D80, D60, 14b's, 404's )
G