Best bet on rear suspension?

The 400 I'm talking about want be a killer horse power motor.... I'm hoping for around 1 horse power per cid.... Maybe a hair over.... I could get that out of a small block easily.... But I like the sound of a big block, plus if I wanted a lot more power later on, I got a foundation to work with, that is as far as displacement goes.... Granted a bit heavier, but heck, this is a light weight A body, not a 3500+ pound car.... So a little heavier motor want make that much more of a difference.... Plus the 4 speed.... Need I get on that subject? As for the Dana versus the 8 3/4, I know the Dana is stronger and bigger (there for heavier), but if I had a choice, since I'm talking some where around 400 horse power, maybe a hair more, the 8 3/4 will work, but trying to find one near me well.... That's a bit of a problem.... I'm not even 100% sure that the rear axle I found is a Dana 60 or not, I only glanced at it for a moment.... But it's BIG, and looks to be a floating axle (could be wrong though, memory aint all to great when it comes to picturing things)..... The Dana 60 stuff is readily available whether aftermarket or not, versus the 8 3/4.... So for now, I'm gonna put the rear axle choices to the side for right now, and concentrate on the rear suspension, topic of this thread really.... And based on the above links that I provided, here's what I got in mind:

The superstock leafs rated at 2800

A leaf spring relocation kit

The Cal Track bars

The above shocks have been decided against upon, need input for others...

Will I need a rear axle shim kit? If so, is there anyway to know w/o checking to see which shim degree is needed? And if more than one, total degree?

I still want to use a screw type adjustable pinion snubber

So, any questions, comments, concers?