87 4x4 questions

A friend of mine recently got a 87 4x4 with the 3.0L v6, and he is kind of wondering about a couple of things

What sort of fuel economy should he expect?
has anyone removed the cat converter and are there any negitive effects from this?
Are there any inexpensive mods that he can do to the motor to increase bottom end power.
And finally he sayes that it feels like it has a posi, or limited slip rear end, was this an option?

Thanks in advance