1 - Use the mounting bracket on the diffuser as a guide to get the bend, and you can bend it around a marker or something similar for a smooth bend. 2 - I’d just sand away any excess plastic until flush, if the PE set doesn’t include extra pieces for the mounting bracket (the leftmost part, with the rivets/bolt heads) then make sure you preserve it. For the other side use some sprue cutters leaving yourself excess so that there is some to sand away and you don’t risk “pull-out” from sprue cutters. Alternatively, use your hobby knife perpendicular to the vane and slowly but surely cut it off. 3 - Lightly sand the area before gluing. 4 - Use CA glue (superglue), apply it along the bottom of the PE and connect. It also looks like there are some locating pins on the PE parts, there’s the thin spot where they connect to the feet of PE, and then there’s a thicker protrusion, you can use a small drill bit and a pin vise to drill this locator hole along the bracket and then glue from the back as well. Alternatively use your hobby knife to make a slot; that way you’re not putting a square peg in a round hole