work table with a sliding top.

A client of mine wants me to make a table for him to use a light table on. he wants the top to be moveable, as in he can slide it out to increase the overhang when he's working at it, then slide it back when he's done. the top is currently drawn at 72 x 32. the base is more or less mission style, with 8 legs framing panels on 3 sides and drawers on the 4th.
I'm thinking I'll use heavy duty drawer glides and stiffen the casework up with a false top under the moveable one. it will need some kind of a fairly positive detent system to hold it in the open and closed positions, which I haven't figured out yet.
the whole thing seems a little goofy to me. I'll be meeting with him tomorrow, and I want to be certain that this feature is really necessary before it goes too far.
any thoughts?
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