There's a book "How to Build Tri-Five Chevy Trucks HP1259" that's a pretty good source of info. Google it, but stay away from Amazon, they want $100 for a $20 book.
If you go to the Classic Performance website, you can download the "instructions" for their (actually Total Cost Involved) IFS to get an idea of what's involved. Custom Classic Trucks also has a pretty good archive of tech articles.
I don't know that there's much functional difference between them and Fat Man, but Fat Man is on the east coast so you can save some $$$ on shipping. I've dealt with both and hands-down the people at Fat Man are way more helpful.
Either way, by the time you throw in the PS pump and hoses, brakes, rack, steering column, brake booster etc. etc., it's going to run into some seious money. But, for me it was TOTALLY worth it.
The word around the campfire is that rear discs are highly overrated.
