Knuckle & lift size question!

[Sooner1970_K10]

I own a 1970 chevy 4x4 that is completely stock. I have been wanting to put a lift, tires & rims on it since I bought the truck last year. Here are my questions. Keep in mind that I wont do much else to the truck for several more years.

(1) Should I keep the stock lift and slap some 31x10.50x15's on the original rims and be content with that for a couple of years?

(2) Should I buy a 4" superlift HD kit (No-blocks) some 33x12.50x15s and a new set of rims?

(3) Should I buy a 6" superlift HD kit (No-blocks) with 35x12.50x15s and new rims?

The way I figure it, the 6" lift kit isnt much more than the 4" lift kit, the tires arent much more and the rims would cost the same. I plan on using a steering stabilizer with whatever size lift I go with.

I know I need a steering arm, what else would I need to do if I went with a 6" lift rather than the 4" lift? I believe I have to get a new driveshaft made or something with a 6" lift, correct?

Does anyone have any pro's or con's for going one way or the other?

My last question is all the lift kits say that I require an (OPEN KNUCKLE) what exactly is this? Is the difference between an open or closed knuckle the boot or housing? I have attached a picture of my truck, maybe someone can tell me as well as point out to me what an open knuckle is? Thanks again.