GM parts direct also says "fits all LS/LT/SS 2008-2011". And they don't list any for 2006-2007.
I got the Fs wrong Getrag/Opel/Italian is F23, Saab/Sweden is F35
I think they changed the final drive ratio between 2007-2008. So different part numbers.
F35 might be better with higher torque but the F23 has a much better interweb rep for price and life. Both fit, both work, dealer's choice. Probably would make a difference if you were going to LeMans.

 

A 5 speed SS, now without limited slip. I think you’re really going to miss the extra traction you had before.

 

From the list of 2009 RPO code description here in these forums, https://www.chevyhhr.net/forums/gene...e2/#post298059

FQ7 Ratio - Transaxle Final Drive 4.05
FR7 Ratio - Transaxle Final Drive 3.95
FR9 Ratio - Transaxle Final Driver 3.29
FX2 Ratio - Transaxle Final Drive 3.91
FY1 Ratio - Transaxle Final Drive 3.63
G85 Axle - Limited Slip, FWD
MM5 Merchandised Trans - Manual 5 Speed Provisions
MU3 Transmission - Manual 5 Speed, SAAB, 76.5 mm, 3.38 1st, 0.70 5th
M86 Transmission - Manual 5 Speed, GETRAG, 5T45-E, M, F23, 75 mm, 3.58 1st, 2.02 2nd, 1.35 3rd, 0.98 4th, 0.69 5th

I've never heard of an HHR SS manual that didn't come with MU3 and 4.05.

No list for 2010 there. My 2010 SS has the follow codes:
FQ7
G85
MM5
MU3

As alway, RPO codes do not necessarily mean the exact same thing across years and models.

I always thought 2.4's came with different ratios than 2.2's, at least some of them.