Guessin' that was a PO mod to accommodate a short-shaft motor at one time. From the pics, the OB appears too low (cav plate relative to transom bottom).
EDIT: No Splashwell! couple that with a reduced transom height elevates the risk of swamping.
Re: Just bought a 1973 Starcraft!!!What model is this one???
If it runs you can use it. But the boat is probably rated for a 50hp+/- and the cut down on the transom looks like its to accommodate a short shaft motor. That 1 looks smaller then a 50hp & looks like its a long shaft motor.
None of that would keep you from using it, if it runs.