Do a search. I posted on a thread a while back on this topic. I added a repro tach in place of the fuel gauge. It's not hard, just time consuming. You will need to purchase a Dremel or Craftsman multipurpose tool if you don't already have one.
The center fuel gauge conversion was a little more difficult because not all of the parts are available. There are two studded clips that hold the gauge in place and two "S" shaped clips that hold the gauge cover to the cluster. You can use the two studded clips on the far right of the dash to hold the gauge in place. They are supposed to hold the cluster against the vertical face of the dash, but aren't really needed. You will have to fab the "S" clips. I used a brass strip I bought at a hardware store to make the clips.
Also, you really need an original center fuel gauge or clock dash to measure the size of the hole to cut.
Don't throw away the stock gauge. There are some easily overlooked parts bolted to the back that are absolutely required to make the new gauge work.