How low can you go?

[rob79CJ7]

First I wanted to thank everybody for the warm welcome. Second, can anybody tell me where to find the information about adding parts from a Ford Dana 20 to give my Dana 20 a lower first gear in 4 low. Any and all info appreciated. My 79 CJ7 has a T 150 tran. =with Dana 20 T-C with model 30 front axle 4.10 ring & pinion, rear axle model 20 - 4.10 r/p trac lock 33x12.50 15's