There is never any piston damage.
Never is a big word and in all the ones I have done there was no damage. I have heard of valves breaking and the pieces embedding in the pistons. If the heads are still on the valves just do a valve job and replace the guides with OE MB and you will have done justifiable maintenance anyway.
At that mileage the front lower right rail (removal requires front cover removal) will be OK (for another 250K). Replace all the head rails and the tentioning rail and have a new motor.
Bosch Master, ASE Master, L1
33 years MB technician