Yep - never do things by half!
I managed to fit parts leftover from a cheap Chinese "Overlord" bridge yesterday evening, so now the bass has strings; it seems to play fine, so that's a result.
The bridge saddles did need a bit of fettling to fit them into the Steinie bass plate (their sides weren't exactly parallel or they had a slight lip at the bottom, so they just needed a tiny bit taking off with a small hand file) but nothing too much.
The tuner does grind a bit, so I'm viewing it as a stop-gap and I'd like to get decent/proper parts instead. (I have got some thrust bearings on order, though they were intended for other basses, so may or may not find their way onto this.)
Next step is the preamp doesn't appear to work; I put in a new 9V battery and plugged in a jack, but the LED doesn't light up.
Fixing that might require a bit more effort.