Anyone know about smallstone?

[ToddL]

I know this is an A/V forum, but I know there are bound to be a lot of smart musicians in here too, so: I have a vintage(mid-seventies?) Smallstone phase shifter pedal. I am wondering if it is possible to add an external on/off L.E.D., or am I best to just leave it alone.
Actually I am interested in any pedal mod if you know where I can find them.
eg. Boss or Korg etc.
Thanks
Todd