disk brake conversion Q's

I've been told that the 73-76 disc conversion from 9" drums actually sets the wheels further apart. (widens the track by a bit) Can anyone confirm this? If so, how much wider is it from flange to flange? Unfortunately I didn't get my stock drum to drum measurement prior to pulling them. Now I want to order up some 4-1/2 BP wheels but if the width is different I'll need to take that into account.