Questions on 1965-1976 full-sized cars

I'm confused about generations of 1965-1970 Chevy full-sized cars. The wiki said that these cars are fourth generation but the 1969-1970 cars have new body styling so they should be next generation. 1971-1976 Chevy full-sized cars are fifth generation. Are the chassis frames any different between 1965-1970 and 1971-1976 cars?

I'm confused about generations of 1965-1970 Chevy full-sized cars. The wiki said that these cars are fourth generation but the 1969-1970 cars have new body styling so they should be next generation. 1971-1976 Chevy full-sized cars are fifth generation. Are the chassis frames any different between 1965-1970 and 1971-1976 cars?

I have a 1973 impala 10 yrs then 1983 buick lesabre 17yrs then 1996 Impala still own it .. the frames are the same .. but then metal welding does some additions ...
my family member had a 1969 olds 98 probably the frame is a bit different.. take pictures and do the measurement ...you should do welding to change the frames ..