Super Stock Springs and Rear End Questions

Is the engine in it?
The ride height can be almost anywhere that you want it to be, BUT it is only right in about a 2" window around where the LCA is sorta parallel to the floor. When it's in the window, she will steer the best and not burn the tires off. Too low is better than too high.
There is a factory spec for this, to help the alignment tech get started.
A change in ride height will upset the alignment, so once it's chosen, get it aligned and leave it there. If it wanders or steers funny, it's not in the window, or something else is wrong;often the tires. Changing tires does not affect the alignment; well it might change the caster a hair, but it won't affect tire-life.
If you're swapping engines, it's probably best to leave the alignment for last, after the chassis is at it's final weight and balance.