If you really want to learn how to build a custom turbo kit yourself then you need to start by getting a copy of Corky Bell's book "Maximum Boost".
Anything over 500rwhp is running on borrowed time with these stock 6.2L's. They were not made for boost. Cast pistons, cast rods and cast crank.
I can help with turbo selection. And they are correct at the end of the day you will not save any money building it yourself. You need to budget $10-12,000 regardless and 6-8 weeks of down time for fabrication. There are no bolt on kits available. Everyone will want you to send them your truck for 2-3 months while they fab one up and install it.
I know the guys well at Fastlane and talked with Nick (owner and guy talking in the video) about doing up a one off kit for my truck and at the end of the day he just recommended going with a Whipple.
I would use the stock cast manifolds and just route exhaust pipes back forward to the turbo(s).
Making all this fit is not going to be easy. There seems to be plenty of room to mount the turbo(s) in front of the engine but routing the downpipe post turbo is going to be tricky.
A single Borg Warner S476 would be a good choice. Or twin Turbonetics 62-1's
Twin 44mm wastegates or a single 60mm.
A good boost controller will be a must too.