Why would tour organizers not like handlebar bags? They're great! They're just big enough to carry a jacket from the morning and a few tools or accessories in, they're easy to get into without completely dismounting when you need your camera for that special shot. If it's safety, nobody is going to unzip their handlebar bag while riding, and if they do crash because of it, well they probably would have done other stupid stuff on the ride as well- like joining a paceline with strangers.

Seatpost racks balance the bike funny and difficult to swing a leg over. I much prefer a handlebar bag for tiny loads.

Oh, yeah- the type of bike--- a well-fitted Randonneur bike would probably be best, slightly speedier but still good for long days would be one of the relaxed-geometry road bikes like a Cannondale Synapse or Trek Pilot. Otherwise any road bike that he could stay on for 70 mi a day would be fine.