Thanks for the fulsome reply @prowla. I had no intention of not keeping it at option (a) "fun mongrel" but it could be restored to (b) albeit with the considerations you detailed. As far as scratchplate goes, Rickysounds makes a 4000 repro one in white, based on a 1973 4000, for £49.99. However, as said, I think option (a) is preferable and what I would have stuck with. As it happens, I just acquired a 1974 4000 (all original, pictured below) in jetglo as I like the simplicity and the sub-9 pound weight.
PS, I am trying to cut my bass collection by one and also to defray the costs of my jetglo 4000.