As for 27-inch tires, there aren't a ton of options but there are 2 very good ones -- Pasela TourGuards, and Continental Gatorskins. Both in 27-inch sizes; both good tires for touring.
One thing to consider if putting a load on an old frame -- a modern rear rack (like a Tubus) is a ton stiffer than some of old noodly rear racks we used to use. In my experience, if you put panniers on an old rack on a not-very-stiff vintage frame you can end up with a bike that wiggles around a fair amount.
If you have the budget, consider investing in a really stiff modern rear rack - like a Tubus. It will help stiffen up the rear of the bike with a load on the bike.