Before answering about regearing you need to know the present ratio. But the answer, even if yes, is still not very fast.
GM used Dana 70HD and Dana 80 axles in later model P30 and similar chassis. These axles from those applications have same bolt pattern (but larger 5.25” center bore). They are also available in useful ratios as well as even faster that you could use. Down side is they only have disc brakes, which then requires swapping to front disc brakes too, so more work and expense.
