The question here is simple: Is it safe to install I9300 ROMs and MODs on Galaxy S3 I9305
LTE devices? Unfortunately the answer is NO. DO NOT TRY TO INSTALL
I9300 ROMs on I9305 Galaxy S3 devices. Why not? Because you risk bricking your device and never getting to use it again.
Actually this is one of the biggest issues with I9300 and I9305. The Android development for I9300 is much more extended whilst the I9305 is not getting enough attention from developers. There is no specific reason for that. Basically the LTE version of the Galaxy S3 is not so popular as the normal version.
However, Galaxy S3 I9305 comes with 2 GB RAM memory, compared to 1 GB RAM memory with the I9300. You see the issue here?People are inclined to buy the I9305 because it has way more RAM memory and that is a definite plus. But in the same time, there are a lot less Custom ROMs for the LTE I9305, any for some users that's a big deal. You have to make a difficult choice here.
Going back to our subject, installing I9300 ROMs on the I9305 device. This is most definitely not recommended. It seems that there are some differences in the hardware of the two devices and I'm not referring at the RAM memory here. So once again, do not install Galaxy S3 I9300 ROMs on your Galaxy S3 I9305 device
However, when it comes to Mods, you could try them. The risk of bricking your device by installing I9300 mods is nonexistent. There is no guarantee that they will work, but usually most of them work on both types of the Galaxy S3.