As fuses have no polarity, it doesn't matter which wire is which. Remove the wire(s) from one end of the #16 socket and connect them to one side of the new fuse holder. Connect the wire(s) from the other end of the #16 socket to the other side of the fuse holder. Make sure there are no bare wires or terminals that can short against anything. You should have gotten a fuse holder rated for 30A, that has wire leads a few inches long. Run them around the side of the fuse box so the new holder is in an accessible location. Put the dash back together and you're done.

When I did mine I went ahead and replaced the whole fuse box with a good used one, mainly because I had it laying around from a car I had parted out. It was a big job, requiring cutting the mounting lugs off the old fuse box with a hacksaw blade without damaging the black plastic frame it fits into, and the swapping all the wires over to the new unit. As you can probably imagine, this took a good while.