1 1/4" is ~32mm and 27" is almost exactly the same diameter as 700c. So I'd run them about the same as I'd run a 700x32.
For my ~190lb road bike+rider weight, if I was on decent roads, I'd probably do something in the vicinity of 70 PSI in the rear tire, maybe 5-10 PSI less in front.

What's your bike+rider weight, what are your roads like?