Since you're using a square taper crank, if you use a cartridge BB you'll be fine with using some spacers with a 73mm cartridge. Myself I have lots of spacers and always optimize the chainline of a given crank to where I want it to be, not necessarily where it's supposed to be according to a book. Cartridges are quite versatile in that way, in that they are self contained units and do not rely on the shell spacing for the bearing adjustment. This takes knowing ones own equipment of course, what rings/cog combos are ridden most. So it need not necessarily be .75mm on each side, get an assortment of spacers if you don't have any. Biketoolstec. has tons.