A picture would confirm it, but it sounds like the Revell Hawaiian Pilot. That kit has been around a long time, and it represents a C 3 cargo ship. Maybe 10 years ago Revell of Germany reissued it in their end opening green box. Those will be much cheaper than the old Revell kit with the painting with the palm tree and the cockatiel..
It has a flat bottom, correct?
The scale is closer to 1/375-400.
It's a nice model, if dated. Keep an eye on eBay, you should be able to get one for $ 35- $ 40.
Definitely you want to keep your dad's model, restored or not.
Trumpeter first brought out their Liberty ship in 2004, so you'll know it's not the one your dad built. I do not know of any plastic Liberty ship kit prior to that, in any scale.
Good luck, a worthwhile project.