Originally Posted by CraigMBA

While I'm waiting for my kit to arrive, I mocked up a pinion and the brass sleeves. I can get a 51 in there no problem. That gets FDR to around 3.72 (51/76), no bueno for GT3, but real close for GT2. And looking at the optional motor mount, I think there's even more room:



If you can get a 52 in there, you're at 3.65 and that's close enough. Plus, you can probably fit a smaller spur in there without adjustment with the bigger pinion.