New to lowering, need some help.

[79SWBchevy]

I have recently acquired a 79 SWB from my grandfather. It has the I-6, not sure what size, but plan to throw it out for a 350. It needs alot of restoration. Anyway, I know I want to lower it eventually and I am pretty confused on how to go about doing this. I've read several fourms on here about lowering and i've got some idea of what to do just not completely sure.

In the front:
Do I only need to buy drop spindels, or a lowering spring setup? Or if neither what do I need?

In the rear:
Everything i've read has been alittle vauge on this. What are hangers and shackles?

I found this on summit and I am a bit confused. http://www.summitracing.com/parts/SUM-G752/

When it says: "relocate the rear springs higher up toward the body, allowing you to drop your rear-end.", does that mean I have to buy something else to finish lowering it, or does this kit lower it on its own?

This is not about lowering but I am also curious, how much alterations will i need to make to the motor mounts when i make the swap from the I-6 to the 350?

Don't hold back on your input, I appreciate all very much. Thanks