The pinion gear gets larger as the number gets smaller. A 4.10 pinion is smaller than a 2,.76. The 8.75 housing is tight with a 2.76 and because of that, no other pinions taller than 2.76 will fit.
I thought there was a lower ratio offered, rare, but a gas crisis/mileage brute force OEM solution. I might have been confused with the as already mentioned, the other rears. But if one was willing to even slightly reduce the effective ring diameter, and still use the same 8.75 carrier, keep the same max pinion diameter, move the new pinion teeth slightly rearward, lower ratios could be found. I don't think it would take much diameter reduction to get to 2.40. In my eyes it was possible. Just thinking out loud.
