How hard/expensive is it to switch out gearing on an A-body?

Do you know what 200R4 means ? 200 lbs ft torque 4 speed. I worked for GM for a while and they changed there trans ID a couple times TH350 = 350 lbs ft, TH400 = 400 lbs ft. then they changed it with the 700R4
700 divided by 2 = 350 lbs ft then 4L60E = 4 speed, longitudinal 60 x 10 divided by 2 = 300 lbs ft, E means electronic, 4L80E same but 400 lbs ft of torque. Your way better off with the torqueflite overdrive than a 200R4. A 4L80 is a TH400 with a overdrive gear 4th.