well, he will need the Blazer oil pan, and pick up. Blazer motor mount brackets, blazer oil filter bracket (with sending units) Im guessing the Camaro distributor and coil. Some little things are different, I just did the swap into my blazer, except i kept mine TbI instead of the Camaro's multiport Fuel Injection. Compare the two engines side by side that is what i did. Dont rush it, and take your time, do it right
I think it's been pretty much covered, but I'll just add this..
For the fuel pump, you can get a sender for a newer Blazer, say an '86 that will accept an intank fuel pump. I did this with mine, but I also upgraded to the larger tank.
You will also need to check the VSS, if your friend has one (if it has cruise), it will be located, behind the gauge cluster, the Camaro ECM may or may not use the same VSS. When I did mine I modified a VSS to work with my tranny, but I am using an ECM out of a Cavalier, so it may be different.
The belt driven accesories may need to be retained from the Blazer or better yet, get them from a newer blazer, but I think there are issues with TB clearance and the belt.
You will need to weld an O2 sensor bung into the Y-pipe, as I believe the 3.1 Camaro uses a single O2 sensor.
That's about all I can think of for now. Once you get into the swap, anything else will become pretty self evident.