Carol,
My daughter has an underbite which I always thought was an overbite
until April this year when I dentist told me I had my facts wrong and
things were the opposite way around.  Anyway, I had heaps of problems
breastfeeding her, she just would not open her mouth correctly  and
after 4 weeks of having to attatch a crying baby (she would cry for
15 minites before every single feed, just because I was trying to get
the attatchment right), we finally had a good feed.
She went on to feed for 13 months when she weaned herself.  As far as
surgery goes, I was told that if the problem is hereditary, she needs
a mandibular osteotomy when she is about 8 (she is now 2) and if it
is skeletal, she needs to wear a brace (external) when her permanent
teeth come in.  I presume there would be some similarities in someone
with an overbite.  Personally I found that no position was helpful,
it was all a hard slog.  The worst thing I feel that I didn't know
that it was a problem with her teeth/jaw until she started getting
teeth and then I could see their placement.  She has a grade 3
underbite, which is pretty bad and will need all her front teeth
capped in the next year to prevent them wearing away into stumps from
rubbing against one another.  I had heaps of suggestions via lactnet
and at that time called the underbite an overbite.  That was a year
or so ago, so you should find something in the archives.
Val in Busselton, Western Australia
IBCLC RN RM