As for the markings, opinions seem to vary! Everyone agrees that there was a white theatre band.
The white spinner would in fact be a partially white spinner, just the front part, similar to the other JG 51 aircraft in the pictures above. This is a good bet, but not certain.
White wing tips? Some of II./JG 51's G-6s in Italy did have them, but some did not. It's about a 50/50 call.
Some profiles show a white or yellow rudder with victory markings. I'm not sure where that comes from as, again, it is not visible in images I have seen. I have a book of rudders (I know, I know) and Rammelt's is not in there. It is so prevalent in profiles and decal sheets that I wonder if there is some good evidence for it which I don't have.
I can't see evidence either way for the undercowling to be anything but RLM 76. If it was anything else it would have been RLM 04, but I can't see a demarcation in the photo.
I know this is all a bit vague! I would definitely do the theatre band and white front to the spinner. I would compromise on the wing tips and do the undersides white. I would leave the lower cowling RLM 76 and I really don't know about the rudder. IF I decided to colour it and apply the abschussbalken, I would do it white rather than yellow. Most of this is just educated guess work and others might have different opinions
Cheers
Steve