Here's some part numbers just so folks can see what I'm talking about.
These all go on 3" tube axles.
3400836 & 837.....Supposedly '70 E-body only (I don't know)
1856346 & 347.....Much more widely used.

The only difference I can see is that with the 836/837, the shock stud is about an inch lower than the 346/347.

Why would 70's need a lower shock mount, is the upper mount also an inch lower ?

Seems like these could all be used interchangeably (unless you just need the correct numbers).