I'm lost and need some help on a 68 C10

[danheit]

Guys, I need some help. I am at a total loss when it comes to some of this suspension stuff. Here's my delimma (I asked in the 67-72 forum, but quickly learned that I was asking about something impossible, so....)

I am supposed to be selling my 55 and 57 pickups tomorrow, going later that day and purchasing a 68 C10 swb manual everything with a 350 and 3spd (now in the floor). I currently have in my garage a full 1990 GMC 1500 Sport frame with a static 4/6 drop, bolt on c-notch, front drop spindles, posi rear, power steering, and all the brake system still attached.

I am on a budget of almost nothing.

Can I, and how easy is it, swap my 1990 GMC suspension to the 68? I have read and searched, and the only info I have found so far is about swapping the upper arms from the 90 combined with c20 lower arms in order to use disc brakes for a 6 lug conversion. I would rather stick with the 5 lug on the GMC, especially being I already have wheels and tires for it. Also, I am planning on swapping in the rear axle if possible and hopefully using the entire drivetrain.

Other question is regarding the power steering gear box. Why do all the conversions show using a 73-87 box and nothing for a later model box? Why can't I use my 1990 box, as from what I can see from pictures, it looks pretty much the same as far as dimensions and layout go. Is it just that nobody uses them because the 73-87 front cradle swap is so prevalent?

Any help will be appreciated!!