I believe you'd have to take out the shorter ones, but not many, no telling how strong old leafs might be after 60 years of abuse, I've had individual longer leafs break - might consider getting mono-leafs if you don't carry any load - the overloads, turf'em or leave'em, won't make any ride difference at all because they're never in play unless you're [over]loaded, just add a little weight back there, which should actually improve the ride
Bill