Get him to put "Sweet Child" in.  The harmonies are awesome.

@Coral

I get what you mean about the voice thing.  The problem with my singing voice is singing really high in my head voice makes me choke.  If you still want to do the song, work around it.

The practice of singing high notes in your chest voice is called "belting," and if you do it properly it's not damaging to your vocal chords (the reason it has a reputation for being bad is that a lot of people DON'T do it properly). 

The key thing to understand is that belting IS NOT FORCING your voice to do anything. If you have to push it or force it, stop, because doing that is REALLY REALLy bad for your vocal chords. (And also it, as you pointed out, sounds awful.) It's also NOT shouting. If you find you're shouting as you try to go up past your first break, stop.

Basically, to belt, you need extreme breath pressure/support and low breath flow (in the same way that singing high in the head voice requires lower breath flow), and you need to open your mouth really wide (watch youtube videos of belters like Stephanie J. Block or Sherie Rene Scott to get an idea of just HOW wide) and, perhaps most importantly, relax. Tension in the head/neck/shoulders will result in a much thinner, less powerful, and less pleasant sound. Pull, don't push (if that makes sense. You should think of the notes as coming from your diaphragm).

You also want your voice placement to be forward, in the mask, as it would be if you were singing in a normal head voice.

Be aware that belting is really physical and takes a lot of endurance. Be patient and build up slowly. Start with just the notes around your break (usually an A flat-B) and work your way up gradually.  

And as always, if it hurts, STOP immediately.

...not that I'm a belter or anything. *cough*uptoaDatlastcheck*cough*

That said, there isn't actually any belting in "Sweet Child." There's a difference between strong head voices and belting (compare the strong head voices in "Sweet Child" to the belting in "Her Voice" [the note on "stand" at a little less than the two minute mark on the OBCR is a good example]. Or, alternatively, go to youtube and find a video that has a bit of both—Laura Osnes singing "Dyin' Ain't So Bad" or Kate Shindle singing "Avalanche" would be my reccommendation—and listen to the difference between their high head notes and their high belting notes [I use these two as an example because they're both have a fairly wide range of regular chest voice/low belting/high belting/head voice—in "Dyin' Ain't So Bad" there are both head voice!D's and belty!D's, and "Avalanche" is similar; DASB is head voice/regular chest voice until about halfway through and Avalanche flops back and forth but is predominately belting and regular chest voice]. Belting is louder and sounds harder than head voices [because it has a tonal quality similar to a regular chest voice, just higher]. And now I will end this extraordinarily long parenthetical statement).  

There IS a tiny bit of belting in the reprise of Sweet Child though. But only a tiny bit.

A general rule of thumb: when you're singing low, think high, and when you're singing high, think low. It's bizarre but it works and it makes for a much smoother transition from chest to head tones, which helps with both belting and developing a mix.  

Oh, and I'd also recommend talking to your director about any concerns you have.