I am working on a boat that was originally rigged with a Bravo X drive and I am trying to find out if a Bravo 1 will work in the existing location or if I will need to rework the transom. Thank you in advance for your help !!

You should have no problem. There was I believe a X, XR, & YZ drives, Only difference was gears and internals. They were all Bravo based.