Erik, interesting advice thanks. I did not know about the Gretsch connection but having looked at pictures of the Firebird on the web I see the similarity. Pictures of the Mk9 details would be most helpful.
I don't know why the current tail piece was fitted but it is certainly not an upgrade!
Yes, the metalwork was all originally gold plated but has largely disappeared from the wearing surfaces.
I'm not sure about how much routing there is under the tailpiece, I will take it off and have a look.
The broken scratchplate certainly needs fixing.
Judging from the colour inside the routed area under the scratchplate I think the original finish was red but at sometime it has been stripped and recovered (not terribly well) in coloured polyurethane varnish. I would consider removing this, but only if an improved finish could be achieved.
There are also currently only three of the four bearings on the bridge, but as you may spot from the photo, the tailpiece prevents the strings being threaded below the bar on the bridge so currently it sits sold rather than floating. Another reason to fid the correct unit. I assume that if I measure up the detailed dimensions of the bearing I will be able to source from a bearing supplier.