Not to step on @Big Dawgs Toyota Tuning 's toes, but I can answer some of these questions for ya!
Our downpipe has a custom V-Band flange with a locating hole for the alignment dowel on the turbine housing outlet flange. This helps ensure proper orientation and alignment during installation. The V-Band flange we use also allows us to retain the OE V-Band.
At the other end of the downpipe, where it meets with the exhaust mid-pipe, we have a custom flange which eliminates the need for the OE doughnut gasket, allowing us a full 3" outlet at the rear of the downpipe. This custom flange will mate to a OE mid-pipe or aftermarket one such as the AWE using a custom gasket we supply with our downpipe. We also supply hardware that eliminates the OE fasteners and springs, so you can securely fasten the mid-pipe of your choosing to our downpipe. Should you wish to make a custom exhaust, we can also supply a custom flange that will match our downpipe, allowing you to create a full 3" system if desired.
As for retention, we've not had any issues, as the addition of the flex coupler in our downpipe isolates the rear flange. When properly torqued (we provide the hardware and torque specs), you should not run into any issues.
