Time to change out rearends.

First off, I have a 72 318 original duster with a 7 1/4 rearend. I'm going to try and tackle taking it out this weekend. Just asking suggestion on how to take it out to make my life easier. I don't have a car lift so she is up on jacks. I'm going to hit all the bolts/nuts with liquid wrench tonight and let them soak.

Second I am putting back a 8 3/4, 3:55 trutrac gears rearend, disc brakes. The car is being setup with a 416 stroker. I'm was planning of hitting 425 horse but let's say we set the suspension of the car up for 500 horse. 727 tranny. Any Recommendation for beefing up suspension to handle the horse power. Will my current springs work or do I throw them out with the 7 1/4? By the way this is a mainly a street car.

Thanks