[EricH]

Originally Posted by Halo4life

If you have access to a horizontal mill with a long enough table, you could just bolt the piece directly to the table and use a 3/4in cutter. You'd have it done in one pass and it'd be almost dead on. Just make sure the piece is square to cutter.

Yep. The problem is, you need 60" (5') of travel. Most mills I've seen have nowhere near that length of travel in one pass.

Now, if you have the sides accurate enough, you could do it in two or maybe three passes. Pass one: one end to about the middle. Make sure the vise or other holder is straight first, though.
Pass two: Move the table back to start. Move the part to the middle, using the quill to help align. Repeat first pass. Do not have the tool contact the metal when you start!
Pass three: Repeat pass two.