I have a bike with a steel fork and a threaded headset/quill stem. I think it is 1". What do I need to buy to make it a threadless headset and carborn fork. Do you just buy a fork and 1" threadless headset and new stem? Is the older 1" a problem? Its a nice bike but needs an upgrade to a lighter carbon fork. Hoping to pick something up cheap on EBAY but not sure what I need. Thanks
Yes, you need a new fork, headset, and stem, all 1". You shouldn’t have too much problem still finding 1" products.
Fork: Get a 1" fork, not 1 1/8". Duh. 
Headset: Get a one inch threadless headset by Cane Creek (I have an S2) or King.
Stem: Get a 1" threadless stem. Many new stems are 1 1/8" but come with a spacer to reduce the size to 1". You should get a stem the same length as you are now using, assuming it is the right length for your current setup.
Also, get some headset spacers from Excel or similar place. Get 4 or 5 different sizes.
Don’t cut your fork steerer until you have your position pretty close, then leave at least 3-5 cms (minimum) after you’ve installed the headset and stem.
I would leave the headset installation and fork cutting to the pros unless you have money to burn.
Good luck.
-Robert
I´m just doing it all: Bought a Reynolds Ouzo Pro Aero in 1inch, a rare Syncros 1 inch headset and will use a DEDA Newton 1 1/8 stem with insert. Looking forward to leave the old threaded stuff.