As a game dev who's been learning ASM recently this was very fun to read through. Wish there was a compiled ROM I could try, but I guess I have to do it myself!
For what it's worth, I was able to simply rename the ET_Fixed_Final.bin file to ET_Fixed_Final.a26 (which might not even be necessary) and drop it into the ROM folder of my Atari 2600 emulator (running via https://knulli.org/ on my Anbernic RG40XXV). It booted up just fine.