Need answers for a 1968 C20 LWB

[lucky13csa]

Hello. I made an introduction in the welcome area last night.
My questions cover multiple areas, so I chose to post this right in the main 67-72 area. Before I ask my questions I want to be clear about what I expect and I want you to know that I've spent 30+ hours browsing this forum with and without the search function. Heck, I think I know everything there is to know regarding working with the C10. Therein lies my problem: info regarding the C20, specifically, is either 1)not there 2)vague 3)confusing or 4) I simply can't find it. Here are my goals:
1)Front and rear disc brakes with hydraboost power assist. I want to either maintain 8 lugs or go 6 lugs.
2)Power steering.
3)Chevy BB/TH400.
4)Posi rear. I have an Eaton.
5)Relocate gas tank to rear.

Now, I imagine 3 & 4 would be similar to the C10. However, 1 is my biggest question. You guys talk about using a 3/4 ton lower A-arms and '88+ ball joints and front brake components along with tie rod ends. The thing is, my truck is alread a 3/4 ton. Will a newer model 3/4 ton front suspension unit(cross member and all) bolt right up? This would leave me with 6 lugs, right? Is my Eaton rearend worth working with or should I get another rear? I want to keep my rear coil setup. How about power steering? Can I use a hydraboost setup from a medium duty commercial truck? How about a gas tank(from a junkyard) that won't hang to low?
If I have to do some fabricating I will. But, the more bolt up solutions the happier I'll be. I just found out last night that I had an Eaton rearend(thanks to this great forum) and I have not researched that yet. Going to do that as soon as I post this. I know that these are a lot of questions, but I have faith in the members of this forum. I would greatly appreciate any answers or pointers in the right direction. I just hope that I will not be answering my own questions($$expensive$$).....LOL. I just got this truck for $300 less than a month ago and I love it more everyday. I have a vision of what I want this truck to be when I'm done. If you made it through this post, thank you for taking the time.

Sincerely, Mike

P.S.- I found out quite a bit about my Eaton rear end. My only question with that deals with putting disc brakes on it. Also, two other things that I forgot to mention: I do not want to buy kits from any companies. I want to do this with swapping parts and if necessary, minor fabrication. Is there and where can I get access to a GM parts # interchange book? Something that lists all of GM's part #. Thank you.