The 6122-58 has a metal nut instead of the zero fret and will not have the wider fingerboard.
1959 was the last year any modifications were made to the single cutaway Country Gentleman. They finalized the bar bridge, half moon inlays, Grover Imperial "stair step" tuning pegs, installed the zero fret and added the "Vee cut" Bigsby.
There were no more changes made to the guitar until 1962 when Jimmie Webster got them to make the "George Harrison" double cutaway version with the mutes and backpad.
My 6122, while actually made in 1961, qualifies as a "59" because of the design features I already mentioned. It originally did come with two standard Filter-Trons.
Chet, as Richard pointed out, added the double bar pickup and rewired the bridge pickup to his guitar. He had ordered one with a wider fingerboard (a little known option at the time) and claimed that particular guitar's fingerboard noted better in many ways than other gretsch guitars. That is likely the main reason he held on to that instrument. It just happened to be a better playing guitar.
He didn't care for the Grover Imperials and swapped them out for the fatter "butter bean" tuning pegs. After years of tinkering different switching combinations he finally took out the tone switch and just left the pickup selector.
THAT is what you get with the 6122-59
I did a lot of modifications on my guitar to bring it up to specs to be as much like the 6122-59 as I could but of course I could not replace the standard neck.
Here's a link to my guitar listing the modifications I did to it. Not only did I upgrade the pickups but I also anchored the Bigsby and made the stringing bar a straight through affair. That, btw, is something I highly reccomend.
http://gretschpages.com/guitars/models/examples/1025/