In order to make the sort of connection you require, I would recommend using our Duraliner chimney system, rather than Duraflex. Duraliner will have an anchor plate to attach to the stove, as well as a slip connector assembly that is designed to attach to a chimney anchor plate atop existing masonry.
The major components are the DuraVent DuraLiner Round Stove Connector for Dura liner 8 inch Pipe
as well as the DuraVent DuraLiner 60 inch Round Flex Reline Pipe
. Lastly, you would need to use the DuraVent DuraLiner Slip Connector and Hanger for Dura liner 8 inch Pipe
. You will notice that the length of Duraliner covers 60 inches; however, this liner can be collapsed an manipulated to fit into the 48-inch space you have. The slip connector can also be cut to shorter length. These parts, in conjunction with your masonry anchor plate, should allow you to complete the installation.