The FE code 335 HP 348 was available in 1959 according to Chevrolet by the numbers reference book. The only difference between the FB code 315 HP 348 and the FE code 335 HP 348 was the 2.5" exhaust manifolds, down pipes and mufflers I believe.
If you go to the 1959 Passenger Car Specs at the GM Heritage Center on the Wayback Machine
you will find the 1959 engine suffix codes include both the 315hp FB engine and 300hp FD engines carried over from late 58 as well as the 335hp FE engine and the 320hp FG engines listed. Thats because there were changes that upgraded the HP ratings accordingly and were included in several revisions to the specs. Only the 3-23-59 version of the specs are shown so you have to read the details and epecially the notes to determine the changes that were made. Those include the aluminum intake for the special cam 4 barrel carbed engines as well as a revised AFB carb for the 320hp engine as well as piston changes and 2.5 exhaust on all special cam engines. Even more details are shown in the AMA Specs for the 59 V8 engines following the GM Specs.
The 305hp HD Power glide engine was introduced on Revision dated 11-25-59 with 11 to 1 compression and AFB carb on a Cast iron intake.
The 320 and 335 hp engines have dyno power charts dated 3-5-59 and were included in the 3-23-59 revision to the GM specs.
The following is from the 1959 Advanced Information publication from Chevrolet Motor Division Engineering Department. Note the 300 and 315 hp engines listed and absence of the 305, 320 and 335 hp engines that were introduced later in the production run as stated above.