Hi mate.
Look up Charlie Hall's Forum. He was Hank Marvin's tech guy and there's nothing he doesn't know about The Shadows' echoes, better than anyone else.

It depends just how accurate you want to be as it can be a very involved procedure.

The best echo units to get the EXACT shadows echoes are:
Alesis Q20
Alesis Q2 plus some modofied earlier Alesis ones

Yamaha Magic Stomp. I have this one and not only does it get the right echoes it even emulates the right amp sound - though you'll have to set your own amp up as well.

Check out my 'Apache' on YouTube. I did it years ago but it's a good example. This was recorded using a Korg AX300G for better amp simulation, and the Yamaha Magic Stopm for the echoes, these then went straight into a mixing desk then to the computer.