Torsion bars

Time to get under the car with a screwdriver and some gumout and scrape the crud off the numbers on the rear ends of your bars...

888/889 .830" 85 lb/in (base slant 6)
890/891 .850" 90 lb/in (base V-8)
892/893 .870" 98 lb/in (HD V-8, Formula S)
894/895 .890" 108 lb/in (67-69 big block)

There were also .920" "police" bars, 1976 only. You probably don't have those. In fact, pretty sure the biggest front bars in 1964 were .850" and I'd bet that's what you have.

I've logged plenty of miles with 9" drums, .850" t-bars and 13" wheels under an early A body. OK for put-putting around the neighborhood, but pretty much inadequate for modern city traffic. In fact, a lot of the reason my car is off the road now is an overdue front end rebuild and brake upgrade (plus a total lack of cash to make it happen).