Shortened driveshaft is a very big improvement, the only noise / vibration back there is also present in my blue BRZ

Happy with the change.
I would prooooobably say I should have left another 1/2" for a total shortening of 5", but it should be fine as-is.
Oh, also, I figured I was on new enough firmware that the fuel gauge was fixed. Fueled with a little under 1/2" tank, I expected to put 6 gal or so in. Took 11.2 gal, lol. I'm on 3.05.1
2x M10 15mm spacers
2x M10x1.25-60 bolts
2x M10 split washers
2x M10 fender washers