I know that chelev and the sciatic nerve are not kosher but what about say eyeballs, heart or testicles? I tried looking but couldn't find the answer. This isn't something I want to do just a random thought I had.
I am not an expert, but I will make an educated guess.
If the Torah did not expressly forbid it, and there is no allusion to it, then it should be permitted.
I cannot find any prohibition from eating those parts (aside from the sciatic nerve, etc) so if you want to, it should be permitted. But there are parts of animals which we normally do not eat.