All '59 models use the same pedal... at least the one in my Invicta & Electra parts car matched. Other years very well may be identical- one pic I just checked of a '60's interior shows the same pedal. Also check Impala parts houses- a number of interior components have been shared across 'divisional lines'... such as the deluxe window/door cranks for '59 were also used in '61-64 Impalas- allowing you to actually pick up the phone & order brand new repro " '59 Buick" parts.... sort of. I do know '59 Pontiac is quite different. Have you tried the BCA's classified?
Just saw your pics your posted a while back. FYI- that's not the right brake pedal pad OR pedal: '59s used a dual-arm brake pedal; that is: there are supposed to be twin arms rising up from the pad with the steering column going between them. Again- just an FYI- if what you have works, it's merely a matter of cosmetics.