Slant 6 to 318 swap, 72 Duster, Using 75 D100

Ok so Im going to be starting a new project and im looking for any info that would help and I have a few major questions that if could be answered would save some time.

First of all here is what i will be using.

I have a 1972 Duster slant 6 that i am going to be throwing a 318 into.
The donor motors are going to be coming from one of the 2

1977 D100 stepside or
1975 D100 stepside
I will be throwing the slant 6 that is in my duster witch has a bunch of super 6 upgrades into whatever one i rip the 318 out of.

Both Trucks have running 318s in them and because I am in California I assumed that the best downer would be to remove the 75 because if i put the slant 6 in it it is smog exempt so i wont have to worry about getting it up to smog standards.

My first of the questions i have is if the axles or the rear ends for the rear of the trucks would match the size of my duster(would they be swappable) i have not purchased the 2 trucks but i will be soon so if anyone has the measurements of the length of the rears that would help.

I have purchased a front disk break kit for my duster and it changes the front to 5x4.5 from 5x4 in the front now my goal is to spend as less as possible to get the rear to the same as the front. One of the trucks has a nice all around matching set of wheels that are 5x4.5.

When i pick up these trucks i am also getting 2 sure grip rear axles and ends so if it is possible to throw the entire axle and end on the duster it that would be great. If not what an i looking at trying to get to throw one of the rear end chunks into an axle that will fit my car?

Also is there anything that i need to know before i do the swap over to 318. any extras i will need to complete the swap? I have these 2 d100s to work with and im picking them up because they are both in decent condition and i talked him down to $2k for both trucks and a lot of 318 parts and the 2 sure grip axles.

Thanks in advance for anyone's help. Im looking forward to starting on this project.

Trent