This has nothing to do with a lifter.
Do you have an Alpha drive? As shrew said replace the impeller and if it's an Alpha this will require a gear lube change which I would recommend anyway.
If you still have overheating issues inspect the exhaust system as it is water cooled. If salt water it will need to be replaced if never done.
Change the engine oil.
Anodes yearly if kept in the water.
His old are the bellows?
1997 2400 SCR
5.7 Vortec / Bravo 2