Completely Custom
The cabinets for the Flair ranges were an entirely custom-built unit with not only trim to match the front of the range, but additional support and structure to support the 230 pound weight of a 30" Flair range or 325 pound 40" models. The cabinet itself was 27" high, lower than a standard kitchen cabinet of 34 1/2" so as to accommodate the pull-out cooktop and give it a working-height of 32".
The cabinet from Frigidaire started out as an option in 1960, ordered separately with the range and proven so popular, then became standard and the range-only was made the option for site-built cabinets. The range only would very rarely have been installed in an existing kitchen, the odd dimensions for the entire unit, electrical connections, etc. would have made it rather cost prohibitive for most of the "replacement" market.
I have the Tech-Talk for the Flair ranges if you'd like to email me, I'll scan the cabinet dimensions, and installation section for you.