Been a long time since I was hands on with a Jazz (even longer with a Precision) and the question of the day concerns neck profiles...
Jazz and Bird necks are the same width at the nut. Are they otherwise similar in thickness etc? I could/can hunt down some Bumpers to try out but I have a thing about not trying out stuff I'm never going to buy on the basis that it wastes people's time and energy.
Not all TBirds are the same.
Some measurements:
My 08 Gibson TBird- width at nut- 38mm, width at 12th- 54mm
My 77 Greco TBird- width at nut- 43mm, width at 12th- 53mm
My Jazzes vary a bit too
Genuine 75 Jazz- width at nut- 40mm, width at 12th- 56mm (70s Jazzes are blocked and bound and deeper through than other Jazz necks- they feel chunkier)
MIM 06 Jazz - width at nut- 38mm, width at 12th- 58mm
FSR Antigua Jazz- width at nut- 38mm, width at 12th- 56mm
G&L ASAT- width at nut- 38mm, width at 12th- 55mm (this is their Jazz width neck- not sure what they call it)
My Greco feels like a P Bass to play, except my P Basses are around 58 mm at the 12th and so the Greco is a little more parallel sided. It also has a flatter fret board than most Fenders. Certainly it feels bigger than a Jazz neck.
The Gibson TBird is slimmer than even a Jazz neck and you can feel it IMO, particularly in the genuine 75 Jazz which is bound and is a little deeper front to back than my other Jazzes, which feels almost like a 70s PBass B width beck to play. The Gibson fretboard is flatter as well.
The closest to a my Gibson TBird's neck is the neck on my ASAT IMO