Same location on my 63" Eaton hubs is 4"; swapping to them would net you 68" instead of 70, I think.
The 65" Eaton hubs measure about the same as your pic, in that same location.
Sooooo... I think you can swap on the 63" Eaton hubs to get down to 68", but assuming that the bearing spacing is the same between your Eaton and my four, (yes, I've got four of them here to measure), you can't get much narrower than 68" on that housing. I think, in order to get narrower, you'll have to swap to a narrower housing, which is what I've got--they come in 63" and 65" widths (65 is pretty common under 3/4T late-60's Chevys) pretty regularly. The 63 hubs that I've got, are off a bigger truck (cab-n-chassis?) but I think you'll only get down to 68" even with later-model 14b CC hubs, and you'll have to do a whole buncha machine work to get there.
My advice, I guess, would be to get a 65" 2WD Chevy Eaton housing and axleshafts, and swap everything else over from your current one, if you want to lose 4" of track. It'll lose you 5", actually... but 5" is closer to 4" off than the alternate 2" drop from using my 63" hubs.
Have I made this clear-as-mud yet?