At a minimum you're going to have to swap out the spindle drive, too. The 440 uses a brushless DC motor/drive while the 770 is a 3 phase AC motor/VFD. I think the 440 uses a 0-5v signal, too, and most vfd's will want a 0-10v signal, which would have to be rescaled.
glockcnc has a 1200w bd setup which should be plug and play , if the shaft size for the pulley and mount holes match . I've got one squirreled away here somewhere , it takes a while to get a motor and driver out of him but it eventually arrives . I bought mine to get an old g0704 clone back up and running but never did . I figured that in a bind it may be a good backup for one of the 440's , even if a couple mods are needed