Quick update...I have purchased a black Schaller bridge from basschatter umcoo..like this:
Something I hadn't realised when I bought the bridge was that it is a 3 screw config which means I may be able to mount it in the exact same position as the current BBOT 5 screw style one with the broken screw head.
If not it should mean that certainly, a smaller adjustment can be made than if it was a 5 screw!
So I think I am ready to attempt the last phase of my build. A refin of the body. I quite like the 'none more black' look but there are a couple of blemishes on the black paintwork which, while not serious, do detract from what would otherwise be a reasonably nice looking bass.
I think the next stage is to use a heat gun and get ride of the black paint and drill the new holes for the bridge.
I am also planning to to do something a bit different for the finish so I will have to figure out how I can do that without 'losing' the screw holes for the bridge and scratchplate - or maybe I should just fill in the scratchplate screw holes and then re drill better ones (some of the screws have to go in wonky).
Oh well - any help or comments appreciated as always and I will post up photos of my progress as I go.