Gear questions

[Crusty69]

I have a 69 with a 400 sbc and 3 speed with 3.73s. During the build I swapped in a new posi but kept the factory gears thinking everything would be fine. I know from the factory the different series diffs align with certain gear ratios but do they make aftermarket longer gears i something like a 3.08-3.27 for the series 4? I hate to buy another posi but my first gear is useless and I’m running 3500 rpm’s on the Highway.