Although the 400 is "tougher" in a sense, the 700R4 is a very nice transmission that can be built to survive harsh punishment (snowplowing, towing, driven' it like you stole it!). You would need to find an adapter to fit your particular transfercase and lengthen and shorten respective driveshafts. Fabricate new crossmember mounts, linkage and a host of other mods. It just doesn't sound cost effective, plus you will be loosing your low 1st gear ratio and overdrive!
My advice, get a thourough rebuild from a custom transmission shop. Install a big cooler(s) perhaps one with a mounted thermostatic fan.
why would you want to downgrade to the TH400?The 400 is tough,but it is inefficient and has a high first gear and no OD.The 700 wil give 20-30% better mileage on average,more if you drive highway mostly.If your having repeat problems,then find a new tranny shop,or buy from a GM dealer,a reman from GM is 1400 here,if you can get shop discount you save 20%,with 3/50K warranty.The money and time you spend swapping to the 400 are a waste.
I did it..i was pulling & pushing snow with mine in a 6.2 diesel..diesel went out , put a 350 in it ...5 months after in a snow storm the 700r4 went out,(rebuild didnt last 2 years rebuilt for $1400 & did the transfer 2 months later for another $1400),but i put a 400 T & also switched the transfer case to a np205. I also had the whole truck to which all these parts came out of & that was a big help...they were all put in a 83 custom deluxe & parts were out of an 80 scottsdale..only real cutting thing was the 4x4 lever had to cut a knotch cuz it was a longer stroke-------IT WAS WELL worth it cuz that 700r4 in my opinion is junk when pulling ect, but i did like the gas mileage & speed, most 700r4's came in the diesel engine they say