Did you test a negative address intentional or how did you get this exception? Your patch doesn't fix the problem. Now you can't access offsets greater than int.MaxValue (2GB). I'm a little bit shocked that y and z are both negative...

var x = new IntPtr(-1);
var y = x.ToInt32();
var z = x.ToInt64();

I expected z to show a large number instead of -1.

I think I got the exception when the program tried to construct a BaseHexCommentNode, presumably dereferencing an address, my file is exactly 2,147,516,415 bytes in size.

I think the problem with this is that when pointer in IntPtr is 0x8000_0000, the ToInt64() operation does not cast bit-wise, resulting in same negative value

I think this should work. The plugin fails to read valid bytes if you try to read after the file, but that's a different issue, I think I saw 64 byte blocks hardcoded somewhere, this might be related to that.

There are some places in C# library methods I really wish that would just accept or provide unsigned values.

I will add a new extension method for IntPtr in the ReClass.NET project to make the logic reusable.