Yes, seatbelts between newer and older models have similar attributes. The main difference is the amount of force applied to the belts and the resulting injury.
You can assume that the earlier lap belts were better than nothing and that the lap and shoulder belts were better than the lap belt only. Then you have the shoulder/lap single belt in the 70's which was superior than either the two prior, yet not as good as the same system in a car without airbags...yet with improved crumple zones.
So, in essence, its about how much force the body applies to a belt system and the resulting injuries. You compare the same exact parameters between a 3300# 68 Firebird and a 3300# 2010 Cruze (no airbags) and the difference in injuries will be substantial.
With the amount of mileage one will see driving a first gen, the possibility is there for a serious crash, but compared to a daily driver...I don't worry too much, if at all about the old school restraint system. I believe the injuries would be similar if one was to install newer generation belts in a first gen, but thats my opinion and is crash type dependant.
If you are concerned with the existing seatbelts, send them out for service and inspection.
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1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
