Since it was nominally called a "touring" bike, I bought 27" x 1 1/4" Panaracer Paselas for my '71 P15 Paramount. They are BIG!
Kind of wish I'd bought the 1 1/8" instead.
I have two bikes that have issues with 1 1/4 and 32 tires- at the brake bridges, so I went with 1 1/8 and 28s respectively.
I had bought some wheels that came with a set of Specialized tires- a "Touring" on the front- that was 27 x 1 1/4 and the "Expedition" which was 27 x 1 3/8. They were so cushy- but they were dangerously old- I didn't want to ride farther than 5 miles from home just in case. But they were cool tires.
Bicycle tire pressure calculator shows how to figure it, I use the 700x32 size for my 27" tires and since most of my touring weight is on the rear I change the F/R% to 45/55. Anyway the point is if you are riding with more or less weight you need to adjust your pressure accordingly, so if I ride with just my body weight and the bike's which would be about 190 and change the F/R % to 40/60 then the PSI drops to 55 front and 66 rear (again I like 5 psi more).
The above figures keep the tires drop ratio to around the idea 15% drop that has been widely recognized as the best drop to use for most types of riding and for most types of tires. Some tires may require more psi than the calculator shows so you have to look at the tire packaging and see if they recommend anything different. The reason why some tires require more psi and tell you so is because one, they know about the 15% drop rule, and two, their tires drop a bit differently than most and thus using the standard calculation will cause their tire to drop too much.