L-Ports

Sure you can bend it.  Go to just about any subwoofer manufacturer's box parameters web page and look at the diagrams...you'll see ports with a bend in them in many cases.  It's much better to have the bend than to compromise the port diameter to make the overall length shorter, and it's much better to have plenty of room at the end of the port inside the box rather than to have the port terminate close to a wall. 

Measure the port length through the center of its length, including through the 90 degree bend, for its total length.  Easiest way:  assemble the port structure, making it longer than spec'd.  Measure, make your adjustment marks, and trim to the proper length.  But if you want to be precise on paper before you start building:  due to the bend, the port will have a long side and a short side.  The center measurement of the port will be half of the difference between the long and short side measurements of the total length, added to the short side measurement.