How large is your subject? How much of the frame do you want to fill? The two will tell you how much magnification you need.
Given how much magnification you need, how best to get it?
The magic formula for extension (from the infinity position) given desired magnification and the lens' focal length is: extension = focal length * (magnification)
I gave the magic formula for extension from the infinity position because 270/5.5 smells like a telephoto lens, with bellows draw at infinity considerably less than focal length. Oh, and by the way, tele lenses perform poorly closeup. And if you can't get the magnification you need with your 270 you're going to have to use a shorter lens anyway.
If you need magnification > 1 and don't use a lens that's symmetrical (and I mean symmetrical, with the rear cell a front cell facing backwards) such as an Apo Ronar, you should reverse the lens. This rules out lenses in #1 shutters 'cos the shutters aren't symmetrical and won't allow cells to be swapped front to rear. #0 shutters are symmetrical so a lens in a #0 is easily reversed. Lenses made for general out-and-about photography usually perform poorly closeup, but since you're going to be contact printing this is more a theoretical than a real consideration. But if you enlarge ...
Before you spend any money on lenses or waste much film, buy a copy of Lester Lefkowitz' book The Manual of Closeup Photography and study it.