I recently got a Wampler Tumus Deluxe for use as a clean boost and have to say it does a great job in enhancing my live Shadows sounds. They do a cheaper model as well if you should be interested.
It is based on the Klon Centur which goes for silly money (£3000 - £5000).
Although it is an overdrive pedal, you can tur n the gain up nearly half way and it still stays relatively clean.
It has become my 'always on pedal' now. It just takes your guitar sound and juices it up more.
I checked out the market to find a pedal to boost for Shads sounds and after much consideration went for the Tumus.
It is pretty much an match to the Klon for sounds and the Deluxe has 3 band EQ added and an extra drive switch.
I have tried different ways of boosting my sound and this is best I have tried. Boost is definitely part of that Sound.