4 speed to TH400?

[freakshow108]

I know this is a regularly discussed topic so i will make this a very specific thread. Has anyone done a swap from 4 speed to a TH400 on a 71 K20. I am contemplating this to achieve low rpms on the highway. Im not worried about towing and the 4wd will mainly be used for snow purposes. I have a TH400 out of a 2WD 71 and i hope to marry it up to a 205 transfer case. I dont mean to waste time on the forum thats why ive tried to make very specific. thanks for any help.