I agree with everyone else as far as getting rid of the closed knuckle front, you can use any GM front from 71 up to 87 and even up to 91 on Blazers and Suburbans. Just make sure the gear ratio matches what you have now. The 73 and later axles are a little stronger due to a larger axle u-joint and no necking down on the axle shafts. Its hard to believe till youve done the swap just how much better your turning radius is...plus disc brakes.. and you can walk into any parts store on a saturday and they will more than likely have what you need for it.
I know some diehards want to keep their truck as stock as possible though and nothing wrong with that. I've found parts in the past at Quad 4x4 but its been awhile since I've oredered anything from them...I'm sure they still have the wiper seal kits but give them a call on any hard parts.
http://quad4x4.com/gm44fHDclosedknuckle1962-1969.html
And this may help you too. [scroll down to page 20]
http://www2.dana.com/pdf/5310-3.pdf