As far as I know TF won’t work on the very old Lefty’s (mk1 and mk2 DLR) which it sounds like you might have, but some more details or pics would be able to confirm which model it is, if it’s a later F800 if might be a one of the later chassis versions or a DLR2.
http://www.tftuned.com/service/9-cannondale
“TF Tuned services and tunes Cannondale forks from 2006 onwards.”
but could be worth asking them, as they’ll work on older Headshoks, and some of the models they have listed on that page (DLR/Jake etc.) are pre-2006.
Tony @Thumbprint is my go-to but then he is only 30mins ride away from me but he will work on anything, he’s terrible at answering emails, and sometimes takes a few goes on the phone if he’s very busy (I think he is on Holiday at the moment BTW and due back after the BH)
One thing you do need to be aware of is that there are limited options with the old DLR models, the can’t take the new dampers so you’ll be stuck with the old ones (spares available but getting rarer…), and they do need a bit more looking after than the newer ones as the bearings are resettable at home like the newer and split ring models.
If you’re feeling brave and have all the parts and tools (there are some specific ones for the older lefty’s) then you can rebuild yourself but not a job for those that lack patience.