I just installed an iPhone 4s screen assembly on an iPhone 4 and it worked perfectly, I tested the ambient sensor during a call and it worked fine too. What I had to do is to remove the two legs at the top and the legs on both sides (I tried to cut the legs but in the end I removed the whole metal thing). The I could use the bottom legs and put the screws.
Andrew, I was thinking to do what you explained, but I would not have actually tried if I had not read your comment. Thanks! I bought LCDs from four different suppliers and all of them had the same problem with the home button staying a little low, but now it feels works perfect with your solution.
To remove the back panel there are two different pentalobe screws 2.3mm and 3mm however on the tools list there is only one screwdriver. Will I be able to remove both screws with the same screwdriver?