If you're not taking any of the engine sheet metal off and you don't have any leaks, leave it alone...don't ask for trouble.
I'd think about the clutch, pressure plate, throwout bearing and pilot bushing as they are hard to replace items...most other things can be replaced without removing the engine or trans.
If you replace the freeze plugs, check for rust/junk in the bottom of the water jacket while you have it open and make sure the drain cock is clear.
Mike B
