Engine hours

Perhaps another 500 hours perhaps 10 season if it wasn't trashed. The engine is often more resiliant than the accessories and other mechanisms of the boat.

If your handy its no bother, if you have to go to a dealer for everything, you might be discouraged.

If it hasn't had a valve job already, when you get it done, she'll be able to burn unleaded. I think the valve sleaves are all that need to be changed to use unleaded fuel. But still use high octane.
I agree--do a compression check. Listen for pinging or clattering while the engine is idleing. A compression gauge runs about $30 and can give you a good idea as to the condition of the engine--rings, valves, leaks in head gasket, cracks in block.
Good luck.
My '84 SN is looking at new rings soon.

The important thing is not what the value is, but that all cylinders are close to each other with no more than a 10% variance between any two cylinders. I cannot remember what a good value is, but 130psi initially comes to mind.

1600 hours? I think it all depends on upkeep, storage, and how you drive it. Similar to a car.

About 3 or 4 years ago I skied behind a mid 80's vintage ski nautique. It was used by a couple of guys at a privately owned lake to ski every day after work in prep for tournaments (it was always tied at the dock, uncovered). This boat was the roughest 2001 I've ever seen. I had to step through holes in the floor to get to the back of the boat. Most of the floor panels were rotted away. The boat pulled like a champ, and the owners claimed they never had to do much to it, never had the valve covers off. It had over 2500 hours on the original meter!

And some boats have high hours because someone left the ignition switched on for a day or so.