the bearings are designed to work with the phil spindle, which is 17mm. the outside diameter of the bearings is 35mm, which allows for a tight fit into the threadless bottom bracket. there is a lot of interference with the phil spindle/bb setup. they are both pretty much exactly 17mm and it takes a lot of patience and a little ingenuity to get them to fit, cross your fingers that you don't wreck the bearings on the install.
i have just recently tried the external bearing phil has, and it works really well, if your ok running a modern hollowtech crank. the bb on my fat has been faced down to 64mm over the years and i have to compensate with chris king spindle spacers, so it works OK but if the bb is 68 i think it'd work fine.