1983 hydraulic engine

Pulling the head will be your best bet. That way you will see and find stuck valves,burnt valves,bent valves,who knows?? also the condition of the cylinder walls.If you find any rust and or a stuck piston, chances are you will have a smoker if you don't rebuild. Not saying you have to rebuild. Hell the truck that I'm driving now I took a chance on .Used 318 water/rust in two cylinders.Cleaned up best I could went thru the heads, put in two used valves,lapped all valves, new seals,gaskets and away we go ! Smokes a bit on a pull when cold but clears up when it reaches opperating tempeture.Uses one quart of oil about 250 miles.. I can live with that.
I call it my High School rebuild.Been driving it for 3 years now every day.
I must say it's nice to see your dedication and willing to learn, wanting to work with you hands. Don't see it to often any more. Good for you !