Campagnolo didn't make 27" rims. You just have a tight tire/rim combination. I have the same rims, with Continental tires installed. I don't remember any particular difficulty mounting them, but because of arthritis in my hands, I do use a bead jack (better than tire irons, as there's no risk of puncturing the tube when installing). VAR makes a portable bead jack/tire lever combination you can carry with you:


https://www.retro-gression.com/produ...tire-bead-jack