45 years is WAY too old for a harness. Cessna calls for a 10-year
limit on the harnesses in the 172; this is a recent change to the
service manual, and I expect they'll demand it for the rest of the
fleet before too long. Further, 1958 belts likely have the
metal-pinching-fabric type of buckle which has been known to slip at
high loadings or to cut the belt off altogether. They're illegal in
Canada.
If you have metal-to-metal buckles and they're in good shape, some
aircraft upholstery shops can re-web and test them for you. Much
cheaper than new belts.

Dan