I think you will do better than the guests with disposable cameras but bear in mind shooting a wedding is a mammoth task and it is really hard to get it right. If they can rent you a nikon D600 and a 24-70 f2.8 lens it should be a great start, if they can get a 70-200 f2.8 (stabilised version preferably) you’d have a very good set up. If you can swing a 35mm f2 lens from nikon it would be of great help as the shorter lens gets a more manageable depth of field at large apertures than a longer lens will. The 35mm will be ideal on your D70 also as a walk around lens and at a little over $300 new it is great value and more versatile in the future than a 50mm will be. Maybe get them to buy you a used lens as a thank you for doing all that work with shooting the wedding? It won’t be that expensive on the used market.
One tip I would give you is to shoot wide rather than close ups as you can then crop the shots to get better framing as that is something your shots in the portfolio is lacking in general. With the extra megapixels you can crop more and still get a sharp shot