rear axle alignment?

[COLTIMPALA]

So I'm in the process of bobbing an M35a2 military truck. This means removing the tandem axle and replacing with a single. I measured from hub to hub but I'm getting wonky numbers that I assume are from the front wheels not being perfectly straight (not the easiest task with a 13k lb truck without power steering). Would it be more accurate to measure from axle housing to axle housing like in this diagram I sorta tried to draw?

 

[1075tech]

You probably could. Assuming your front axle is straight. I've only ever measured form hub to hub

 

[Scsmith42]

If it has front leaf springs, I’d also consider using mounting bolts / rivets for the rear spring hangers to measure from.

 

[ronn47]

The manual for my M38A1 shows frame measurements from various points to square the frame.
If you have a manual look to see if that info is in there somewhere.