Markus,
Great research as usual.
According to Auto Atlanta Porsche the Porsche part number was updated to
99610504172.
Using the 99610504172 in your excellent INA reference you provide this updated Porsche # is INA 268902 Ventilstößel or 420 0104 10 Ventilstößel
This crosses over to BGLA #HL6330 on Rock auto. So many 'translations' bothers me......
Here is a previous attempt to understand this opaque issue:
Lifter replacement/upgrade/fix - Rennlist Discussion Forums