Disc Brake conversion... a little help.

[~Whitey~]

I have a 69 c10 that I'm wanting to do a disc brake conversion on... During the conversion I am wanting to add in some 2.5 inch drop spindles. LMC has drop spindles for 67-70 and 71-72. I've research the boards here on this as best as I could and have come to the understanding that the 71-72 trucks lower arms use a little bit bigger ball joint... ???

Here's what I have in parts acquired for this conversion taken from a 72 c10 truck:
Upper and Lower arms
Calipers
Rotors
Stock Spindles
Master Cylinder & Booster
Proportioning Valve
Drag Link and Tie Rods

One again my truck is a 69 c10

Questions:
Should I use both the upper and lower arms from the the 72?
Or is the upper arms the same for all years on the c10's?
If I use the 72 lower arms then I assume when I purchase the drop spindles I should get the ones for 71-72 trucks ??

Thanks in advance fellas and sorry if this has been answered somewhere else already... love the site and I get ALOT of inspiration here.