First of all, 6 and 8 cylinder injectors look identical, but the thread is different. The 8 cylinder has a finer thread. I just installed new injectors in my 88 300CE 103 engine. The part number is 0 437 502 047, the last one that you mentioned. I am pretty sure that those are the ones you need.
The seals are the same for 6 and 8 cylinders. I'll try to find the part number and post it later.