So, as luck would have it, I was only aware (as well as everyone else online it seems) about the LS 4.266 FD ring gear (64 teeth) having the B16/LS inner ring gear diameter of ~110 mm.

The one sitting on the bench right now is 64 teeth and 117 mm inner diameter, which fits the GSR/ITR diffs.

Only reason I caught it was because the owner broke a 4.9 FD, and was replacing it with a 4.400 he purchased used. So now, I get to explain to him that the seller is either stupid or lied, and why Honda would even make the 64 tooth ring gear to fit the ITR/GSR diff.

WTF, Honda???

Aquafina, Mistabone, Synchrotech... anyone else see this before?

 

After some searching, thinking it might be an H22 4.266 final drive. Ring gear has same inner diameter as the outside of the GSR/ITR diffs (117mm).

 

Yep. Owner was definitely sent a Prelude ring gear and an unknown countershaft (15 tooth). lol Could be nearly any countershaft. I just didn't realize the Prelude diffs had the same dimensions as the B-series.