a '79 3/4 sub should have a 10 bolt fr axle. i belive it was '77 when the D44 was phased out of the sub line. but as been mentioned- never say never with squarebodies, a lot of "did'nt make it" is common on these trucks.
have a look at your diff, round-ish cover and "ears" on the bottom of it will be a 10b
View attachment 151331
a D44 looks pretty much like a scaled down D60
View attachment 151332
compare these pics with what you have. both are about the same for strength and durability.
my ''76 K5 blaze had a 400 sb wit a 203 case, but a T350 trans. i used a Milemarker kit to change the 203 to part time. very simple to do and about a 150 clams. nice thing about converting, you now have 2wd low, and a little better mpg's. as the 203 is splash lubed, you will need to run 4by every now and then to keep everything slippery if you part-time it.
the 400 is a decent block. lots of torque- not so much for hp. again as mentioned, they do have siamesed bores so temps are a good thing to watch. head gaskets are easy to pop on 400's.
usual mods will wake up a 400. all i did was add a good intake and carb, freer flowing exhaust and an Isky super cam. power jumped to around a "whopping" 250 horse, but it was a real torqueasaurus- prob in the neighborhood of 400 lbs.
View attachment 151334
first mod i would do is add some rear airbags....subs always seem to have a saggy butt. don't know if yours has it, but i got rid of the carpet in the back of mine and went rubber matt- way easier to clean up if your going off road. and if your going off road, you will most likely want better lighting, i would add relays to your headlights, or LMC has a harness now for like $25 bucks. it will make them old lights shine. other than that i would use it and see what you really need...or want...
Shop from thousands of parts and accessories to help you restore, maintain, and customize your Chevrolet, GMC, Dodge or Ford truck or SUV. Keep 'em on the road with the right part, right price, right now.
www.lmctruck.com
and always been a sub fan. my old '75, never insured it for the road, just used it for bombing around the back 40. an old set of springs from a diff project and some knarly 33's and it would go most anywhere...
View attachment 151335