Most important is to take note of which direction you have to turn things when removing the existing BB, in order to determine if Italian or English thread (hopefully not French or other standard). You can measure if you want, I suppose. 68mm= english, 70=italian

Check with new crank manufacturer to determine appropriate BB spindle length, however. I have some Campagnolo doubles that require 102mm and some Shimano triples that like 113, for instance. Wrong size may throw off your chain line.