i was under the impression that the driven element length effects the resonant frequency, and the gamma match is there for impedance matching, 50ohms.
here is an internet quote from http://www.dx-antennas.com/Gamma_match.htm "The Gamma match is the most used matching device used for yagi beams. ... A well designed yagi has for that reson an impedance around 20.. 25 ohms. A Gamma-match can match impedance below 50 ohms right up to that 50 ohms wich your tranceiver wants to see." (spellling errors are left for your enjoyment)
i would think you may need longer elements on the driven element to lower the freq. a bit. are they the same length as the older arrow antenna that you have? you can probably get an extra set of driven elements, or the whole thing with match, from arrow? or get a set of the reflectors and trim them down.
or just get some arrows, mine says "Easton JAZZ 1816 lite" on the elements https://www.eders.com/easton-xx75-Jazz-arrows-1816-spine.html?gclid=Cj0KCQjw...
73 K F o G cm88pk santa rosa, ca, usa