If you really want this gig, you should learn all of their tunes you can listen to. Learn them as well as if you were there when they wrote them. Learn them inside out and upside down and work on some cool parts you can put in there to make them sound even better. As long as you have an amp that sounds OK, don't worry about the gear. You can buy that later. If you make it sound like you are the only one who can play those tunes as well as them, guess what? You will be playing those tunes and more with them. There will not even be another choice of guitarists in their mind. You will be the ONLY choice for them.