This is a difficult song to reproduce on the guitar for a few reasons.
Firstly, there are several overdubbed guitar parts on the original. I'm
fairly sure that these all use the same tuning but they don't play exactly the
same parts, so there are contrasting notes and chords which thicken the sound.
This is especially true in the introduction where there are (I think) four
different guitars playing. The differences between the guitar parts give a rich
texture to the introduction. There's no way to get quite the same sound on one
guitar - what I've written out is the "essence" of the introduction, which
should give the overall feel and sound of the intro.

More importantly, the original recording uses 12-string guitars. As usual on a
12-string, the lowest four pairs of strings are tuned in octaves and the top
two pairs are tuned in unison. This means that the upper octave string of the
3rd pair actually has a higher pitch than the top pair of strings. In other
words, on a 12-string tuned to CACFGC, when the open strings are strummed the
highest pitch you hear is the F that comes from the high-octave string of the
3rd pair. This pitch is higher than the C of the top strings - it's equivalent
to fretting the top strings at the 5th fret.

So what does this all mean? Playing the song on a 6-string guitar won't sound
quite the same because the higher-octave notes from the 3rd-6th strings are
missing. In particular, on the barre chords like 555555, the top note you hear
on a 6-string won't be the same as the original - the octave strings on the
12-string make the difference.

For some parts, a 6-string will sound almost as good, but for other parts, and
the introduction in particular, the high-octave notes from the 12-string are an
important part of the sound. If you try it out, you'll see what I mean.

One way to approximate the 12-string sound might be to get a friend to play the
same part but 12 frets higher! (Maybe not very easy though ...!)

One other variation on the guitars used for the original (just to make things
*really* complicated!) is the fact that of the 4 guitars audible on the intro,
3 of them are normal 12-strings and the 4th sounds like it has *only* the upper
octave strings for the 3rd-6th strings. In other words it's a 6-string guitar
9in CACFGC tuning) with the bottom four strings tuned an octave higher than
usual. I haven't tried restringing my guitar with the right strings to try this
out, but it might be fun!