I don't know about other Dana 70 axles, but the 70HD I used from a late 80's Chevy P30 chassis is a great swap.
The axle tube is the same diameter, so you can use the old u-bolt saddles.
The spring perch pads need to be each moved out exactly an inch. Not difficult with a grinder and a welder. I recommend tacking them after loosely installing the axle in the complete truck and setting pinion angle, then take it out for final welding.
The width works with no tire fitment problems.
Ratios are available from 3.54 to 7.?? or perhaps even slower.
The downside may be that a Detroit Locker or an ARB are your only choices for a locker. The Detroit is good, but not for everyone and every situation. The ARB is great for everything except price.
The wheel bolt pattern is exactly the same, so the old wheels work.
A big downside to the axle I used is the disk brakes. I love them, and am glad I have them, but they require that you have disk in the front, and that is a task not so easily tackled.
As for the 4-53T, they are not at all hard to find. If you want one in great shape it will take some looking or rebuilding. To find a good one at a great price takes lots and lots of searching. It is not a simple swap. I will have hundreds if not thousands of hours in labor in mine before I am done. Not to mention the many thousands of dollars for all the parts and pieces it takes to do a professional job.
Grigg
