Seems like all the ones I picked up over the years had that Deep U profile. I remember in 1966 when the new Fender Jazz came out with its bar markers and white binding on the neck, what a pretty bass it was. Then when they pulled it off the wall for me it had that deep U shape. Was still narrow but fat (deep). I hated that and couldn't figure out why they did it. I'll never like a neck like that. But you know, you're going to make me start looking at P-basses if there are a lot that have a slim neck. I know there are letters to designate the various necks they used (A, B, and C I think). Do you happen to know what letter designates the 1.58" nut width and the slim profile?