Maybe try to do it using some logic:
Do a compression test to see how the ring and valve seal is.
Check the timing chain to see if it's stretched.
How is the oil pressure?
Is is smoking on startup, compression braking or acceleration?
Does it use oil and how much?
After you have this information we can make informed advice.
Just because the engine has 100,000 miles does not mean it requires rebuilding but it might.