They look like an IC, but taller, like a relay that plugs into a DIP socket. See
http://www.datadelay.com/ . There are different kinds to select from, ranging from rather crude, to rather cool digitally programmed ones. The data sheets are pretty clear and not complicated. I think I would chose a part with a parallel programming input that can take the programming word by DIP switches or a jumper pin header, instead of a serial input which would require the computer to be operating to change it (and changes during operation may produce a glitch that would crash the computer since we're talking about putting it in the clock line).
Edit: For a quick-n-dirty home-made one, you can also just put a tiny trimmer resistor in series with the input of a Schmitt-trigger gate. The RC formed by the trimmer and the input capacitance of the gate gives a delay that is variable as you turn the trimmer. You'll probably want a trimmer that maxes out at about 2500 ohms. The delay may not be super consistent, as the gate's input capacitance and thresholds might change depending on temperature, but it might be ok since we're not talking about an application that needs super-high accuracy, but rather one that can probably tolerate several percentage points of wandering. For example, if the adjustment range were 20ns, 5% is 1ns which should be totally fine.