Many thanks everybody for the replies.
I realise this is a subject that has been done to death over the years so appreciate that people have taken the time to give me advice.
Looks like a trip to the DIY place is in order for some Vernier calipers, a threaded rod, some washers and nuts...
I have 2 options for the fork.
1) Steel, 1", threaded, ex-Peugeot Competition 500. I think it might be Columbus Thron. It's heavy and the (purple) paint is in poor condition. Here's a pic of the back of it:
2) Steel, 1", threadless, ex-budget mid-90s race bike, no-name. Silver and in very good condition.
Here's a pic before it was swapped out for a carbon one:
I am pretty sure that crown races are insatalled on both forks.
I also have a threaded to threadless adaptor, with a shim, so I am not 'restricted' to quill stems if i decide to go the threaded route.
I'm basically ineterested in whatever is going to be the easiest and cheapest solution really, and i am very keen to have a go at it myself to improve my limited skills and widen my knowledge base.