Hi Dean, I have the same boat (97 25ZX) with a fuel injected 502. Congrats. Depending on the condition of the boat and trailer it sounds like you got a smoking deal. I have never heard of one having a 454, time for some forced induction.lol What prop is on the boat? I'm guessing you are going to need to run a 23p 4 blade prop to get that boat out of the water with any weight in it.
Have you had a mechanical survey done on it yet? If not you will want to have the drive pulled and checked as well as the motor compression checked. Might want to go ahead and have the plugs changed at the same time and it wouldn't hurt to replace the impeller for peace of mind. There are not any issues of dry rot that I have ever heard of with that boat, unless there was transom damage at some point and it was sitting in the water.
Donzi 18C
Donzi 25 ZX "Full Tilt F/B "