I recently did this, and all the guides I could find involved using an aftermarket shell. I figured I'd add a little additional guide showing what I did to get this into an original shell.
I did this with the v5, laminated, IPS screen from Hispeedido.
Here is how it turned out.
And here is what the GBA looked like before starting. Sad, isn't it?
This video has all the details, I recommend watching it.
They also have a written guide which is a good reference. But they use an aftermarket shell which requires no trimming. Here is how I trimmed my OG shell...
To trim the shell I recommend a small pair of snips and a small file. I got my file from this set. I don't know where I got the snips, but something like this should work.
Don't use a dremel or any power tools. They will be hard to control and likely take off too much or get away from you and cause scratches. You want to take your time and go slow.
You will need some kind of compressed air. Please don't skip out on this! See below to see what I mean. I used this portable electronic compressor which works very well (I got it here), or a can of compressed air will work too.
You will need to trim all four sides of the screen opening.
I trimmed off all of the left side, quite a bit from the bottom, and about a millimeter off the top and right. Don't worry, there is still plenty left over for the screen to adhere to.
For the left and bottom I used the snips. First make a bunch of small cuts with the snips.
Then from there the small pieces will snap off pretty cleanly with a little pressure.
Just keep gradually filing down the shell and test fitting. Take your time. Eventually the screen will pop in cleanly. You don't have to be totally precise expanding the opening, as the screen will lay into the recessed area the outer bezel goes in. This outer bezel recess will enable the screen to line up correctly. But with that said the more precise you are, the better.
On the inside of the shell, at the left side of the screen, is a ridge you will need to trim off. This can be done carefully with the snips. Just take your time and cut out little pieces, gradually removing the ridge until it is completely gone. Be careful not to cut too far or else you will cut through the shell.
Sorry, I didn't think to snap a picture of this ridge from the back side :( But here it is circled from the front side.
Once a test fit works well and you are done trimming, you will need to remove all shavings and debris from the shell. Make sure to scrape out any straggling bits with your fingernail or one of the small screwdrivers. You want to get the opening as clean as you can. It won't look great, but no worries, the rough bits will all be covered up.
Hit the shell with compressed air liberally. You want to get out every single spec. If you don't you run the risk of them working their way onto the screen. Also don't take your GBA to the beach, ask me how I know...
By the way, see how it says "peel off this film before install"? It is better to leave it on and peel it off after the install is completely done.
The tri-wing screwdriver that came with my kit was too big. It was very frustrating to use. If it is all you have, just take your time with it. Stripping the head of a tri-wing screw would be bad news.
When screwing the PCB back into the shell, here are the holes you need for the screws.
When reassembling, the speaker can be a real pain. I found if it is mostly in place but not quite all the way, stick one of the small screwdrivers that came with the kit in there and push it into place. I actually found the speaker the most troublesome part of this mod :)
Have fun! If you have any questions, you can reach out on Bluesky, Reddit, or email.