I'm confused, are you looking for a neck with a reverse Jackson headstock like on the Robin Medley, or do you just want a better replacement neck with a Fender headstock?
While there is an option for a 24 fret neck like the Medley, you can't use that on the Jeff Beck or any std routed Strat as the extra frets will overlap the neck pickup routing.
As it seems you have access to a Robin Medley guitar, check the measurements/other info on this page:
http://www.warmoth.com/guitar/necks/necks.cfm?fuseaction=back_profiles
as to neck thickness/shape as compared to it to order appropriately.
Any neck you order from Warmoth should fit the Jeff Beck strat, EXCEPT a 24 fret neck.