I got two new heater cores from two different places for mine and neither of them fit like they should have. The original did not leak so I put it back in. I used the kit listed above and in all I have about 16 hours in that one box. I had three cracks I had to patch up on mine. Take your time with it and don't rush it. Also take more pictures of it than you think that you need too so that you know where everything goes back to. I didn't and from when I took it apart to when I put it together was 4 months time difference.
My only question is the resistor looking electrical item that mounts on the box, I am in need of a new one and I cannot for the life of me find one online. What is it?