Edit: I just realized this is an11 year old zombie thread the previous poster just revived. I'm leaving my reply up in case it helps save another CUCV sometime in the future
Honestly I would not spend the time to do that swap on a 1009. A 14bff is a monster of an axle, that is extremely heavy and has poor ground clearance. It's good for heavy duty work trucks and serious off road buggies, and not much else in my opinion.
I have 33" mud tires on my M1009, and wheeled the stock axles for many years with no problems. I swapped the rear out for a 12 bolt (weaker than a 10 bolt in my opinion due to worse pinion bearing design) because that axle had an air locker in it and I wanted the locker.
Now I run 33s, air lockers front and rear, SM465 manual trans, and the way I drive I break 1-2 front axle shafts a year. I've never broke the rear, and without a locker it'll be even harder for you to break it than for me.
If I were to go to a 14bff, the housing has 2" less ground clearance than a 10/12 bolt. So I'd need to upgrade from 33" to 37" tires just to keep the same clearance I already have, and add 200 lbs of dead weight in the axle (plus maybe 250 lbs of heavier tires). In my opinion a 14bff is a downgrade on an off road rig with anything less than 37" tires, and only works with 37s if you shave the bottom an inch or more. You really start getting some value out of it when you start talking 40"+ tires. At that point you definitely need at least a D60 front, you've cut off most the fenders so the tires will clear, and you are doing trails so hard you are basically guaranteed to smash the remaining sheet metal eventually.
If you're gonna build a rock buggy, start with a thrashed civvie blazer and put an LS motor in it. If you just want a fun cheap truck to get out in the woods and drive around with good mpg, run 33-35" tires on the stock 1009 axles and regear to somewhere in the 3.73-4.56 range depending on your tire size and transmission. The truck will do anything you ask it to and will be way lighter and have better clearance than if you install a 14bff.