Dawes Super Galaxy Touring Tandem

I have no idea how these old headsets work. Threadless/ahead all day long. easy to find some nice silver-finish spacers?

IME You just need 1" headset spacers. I've also used a black one and a carbon one before, which if they're thin I think sometimes gives a nice contrast.

yup (well, not 100% but I don't see what I could have missed off). the old headset was a little agricultural.

If there's a huge gap I'd probably trim it, but leave enough to have a small spacer and make sure you're not limited later.