Sometimes you can be too specific in your search, and thus miss threads with lots of information.
The IFS design you are referring to is essentially the same from '63 through '87 and even later on full size Blazers and Suburbans. '71 happens to be the first year they had disk brakes. Much of the information you'll see will say '73 to '87. The design was used more years on both ends.
Mobileortho and Weeds amoung others have both posted pictures of this swap. Steve Andereggen Jr has posted some information and a link to his article on the swap. Joe Way used to post here but I've not seen him in a while, if you can find his pictures online his 3/4-ton swap seems to have come out very nice.
I'm working on the same swap for my '55 1st GMC 1-ton and have started a few threads on the subject. I'm using the IFS from a '72 C20 on mine. I've posted some pictures, but don't think I've updated recently with photos of my suspension mounts. I'll probably do that once I complete getting the steering box in place.
Limiting the discussion just to AD trucks, the frame design is different enough between 1/2-, 3/4- and 1-ton trucks that you really want to be sure you're getting detailed information correct for your truck.
I've crawled under a number of trucks with this swap and have photographed how they were done. Some of them frankly scare me and I would prefer then never be on the road. Others appear very well thought out and professionally executed.
Based on my own research, including talking to one guy who made the swap about ten years ago and who has driven the truck tens of thousands of miles, this is a workable swap that can result in a very drivable truck.
BUT you need to understand the limitations of this approach and its only right for you if it matches what you are trying to accomplish. My own opinion is that this is the wrong way to build a lowered truck. If that is your objective there are much better options. If you don't mind stock height and want a truck when you are finished, this is one of the better answers.
One more tip based on my research: Mounting the steering box in the correct position relative to the IFS is critical. Get it wrong and you will have bump steer worse than any straight axle. The key is to preserve the relationships in each axis with the IFS crossmember.
Those are just my inital thoughts as I looked at your question. This is one of my favorite topics and I'd be delighted to engage further in talking about what I've learned and what others have learned about this approach.
One last tip: When someone tells you how to do it, ask them how many miles they have driven their own truck with the completed swap. While I've yet to drive mine, asking that one question quickly cleared up for me some of the contradictory things I heard from people claiming to know how to do this one.
