Well to be honest, I wouldn't feed Iams to anything. Not only do I disagree with their research methods (barbaric, horrible and cruel), I don't think the food is very good quality. I also don't agree that a specialised 'puppy' food is necessarily a good thing.
I feed our girls (3 labs - 10yrs, 5yrs and 5 months) on Burns food - it's expensive, but good quality without lots of cheap, hard to digest filler and additives. There are lots of other good quality foods out there too - James Wellbeloved, Pets at Home do a brand called Wainwrights which has good reviews - see here for more.
Dedicated puppy food has very high levels of protein and fat in it - some with protein as high as 30% - which are there to promote growth. And that growth can be very fast with that much food going in.
I have chosen to feed a lower rate food to my girls so they grow at what I think is a more natural rate (puppy food is a new, new thing - and def doesn't exist in the wild), giving them chance to build up supporting muscle around their delicate bones and joints. I worry a lot about fast and sudden growth and the longterm effect on joints and as I work my dogs healthy joints are very important indeed!
I know not everyone will agree with my views, but I am a bit -sad-- evangelical about the food I put into my girls.
Your gorgeous new puppy will probably have Mr Whippy Poo for a week or so as he adjusts to the mammoth change he's had - but keep an eye on it after that and it'll give you a good idea about how easy he's finding it to digest the food.
Also - does he really honk? That can also result from poor quality food - I can smell a dog that eats Bakers Complete from miles away! A soothing bath with gentle dog shampoo in a couple of days time won't hurt.
Hope you got some sleep last night!