Re: 75 camero frame w 54 sedan delivery above
1) As a 54 sedan has leaf springs (i believe) then no, a 1996's rear axle will not bolt in. You could however make it bolt in by welding spring perches to the axle at the right widths.
If i may so bold, i feel you personally, should get a professional to do this if you decided to go this route. i do not wish to specify my reasons for the recommendation.
2) i would be willing to bet none of this can be installed in less than 40 hours. i would be willing bet money on this. More like 300+ hours and this is another reason why carbs, distributor, and no computers is so attractive.