If the ground wire is between the wood top and the felt pad, you tailpiece and strings will not be grounded. Make sure that wire is in direct contact with the metal surface of the Bigsby - you will probably have to remove a felt pad in that spot - and then reinstall it over the mounting screw so that it sits between the wood surface and the ground wire. Run a new ground wire from that additional hole - solder one end to the ground wire from the pickup wrap the other end around the mounting screw for the Bigsby. Remove the bridge pickup - you will see a ground wire attached to it (that ground connects to one of the threaded shafts for the stop-bar stud bolt). The easiest way to do that is to drill an additional hole through the top about 1/2' - 3/4' directly behind the (new) mounting screw hole on the handle/spring side of the Bigsby. Keep in mind - you will need to run a new ground wire to the Bigsby. If you decide to install a B7 by itself - you should be fine with mounting screws drilled through the top without a center block. They come in 2 sizes, so check the ordering instructions to make sure you get the right one. The other question is a matter of you like the looks of it. They fall under these three Bigsby models. The Epiphone Casino is a thin-line hollow-body electric guitar.

It will add a couple of ounces to the guitar's weight (4-6 oz.?). Following the method of design for each model by Bigsby, the B-3, B-7 and B-11 are often recommended for the Epiphone casino. It eliminates drilling holes AND it assures the Bigsby and strings will be grounded. For a Casino - assuming you now have a stop-bar tailpiece - a Vibramate V7-335 is clearly one option.

Installing bigsby epiphone casino