Thanks for the relies. My 63s have been re-built by One Thing, so I assume the crowbar will have been changed to later versions or otherwise modified, so therefore wouldn't be a problem. I'll check with OT first.
I'm tempted by the Supernait as I've heard it's had great reviews all round, and it'll significantly reduce my box and wire count, which has to be a good thing!
I'd better try to get to hear one!