How would you ground this bridge.

Drill a small hole from control cavity to under the baseplate run a wire from the usual back-of-the-pot ground and ... usual practice is to leave a loop of bare wire to be crushed between the plate and the body ... Me being a maniac might attempt using a very large hot iron with a bit of flux and tack soldering the wire to the base plate. If it's gold plated that'll go. If it's chrome then it would have to go to the base metal if it's brass or steel.

 

I do the smoosh method, but it goes:

Body - Bare wires - piece of shielding tape (conductive on both sides) - bridge.

 

I have a roll of thin copper sheet that I use in situations like this. I cut a pad about the size of a dime or nickel with a little tail on one side. I solder a wire to the tail and fish the wire & tail into a previously drilled hole. Then mount the bridge sandwiching the copper pad between the bridge & the body.

 

I'm with you on both points, yes, the wire mash seems to work but there's a sort of rock solid aesthetic that it lacks. Hell, drill and tap for a ground screw.

Let us know how the spring loading works out.