Another option for the gears might be Huret Jubilee which I forgot I had in a drawer at work:
I’ve never used it because I don’t have the shifters and there’s a critical spring missing on the front derailleur. This one (thanks random eBay pictures):
It serves a double function really, it does the springing but it’s also the inner parallel linkage. Without it the mechanism just loosely flaps about.
Lunchtime I decided to raid my pal’s box of scrap mechs etc. to see if there was a similar spring I could use. Found one on a later Sachs mech that might work:
It was close, but not quite long enough to wrap round the pivot. I also found a Shimano one which is a bit of a cludge but might work:
It’s not quite as tight as I might like it, but I might be able to make up a bit of something to take up the space between the spring and the pivot until I find a proper one.