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Yes.....the entire rear section of the frame is different to accomodate the difference between the chrome bumpers of the 72 versus the rubber bumper mounting system of the 76. Otherwise they are very similar.
1968 - Original C-3 frame. Remarkably similar to a 1967 C-2 frame; but that is another discussion for another time. #2 and #3 body mounts are open sided cage nut design welded in two locations. A kick-up support was added in the middle of production to add necessary support to the rear portion of the frame.
There were 28,566 cars manufactured in 1968. Data is incomplete or inaccurate on the mix of manual and automatic frames. Two hidden captured nuts were assembled inside the side rail and one long bolt was used through a hanging bracket.
1969 - Slight inner front horn change made; reinforcement in the kick-up area of the frame was used for the full year and continued. Rear most cross member changed slightly. There were 38,762 cars manufactured in 1969.
1970 - the same as the 1969 frame with a very minor change to the rear most cross member. There were only 17,316 cars manufactured in 1970 due to a factory strike.
1971 - the same frame as the 69 and 70. In 1971 there were 21,801 cars manufactured.
1972 - the same frame as the 69, 70, and 71. In 1972 there were 27,004 cars manufactured.
The 1968, 1969, 1970, 1971, and 1972 frames are all interchangeable.
1973 - In 1973 the front inner frame horn was modified to accommodate a new front bumper extension and design for the front polyurethane bumper design. The kick up area, body mounts, and rear cross member were all left unchanged from the 1972 frame. The #2 and #3 body mounts were lowered to accommodate new rubber bushing body mounts. You can use a 1973 frame on a 1968-1972 car with an inner front horn change; and you can use a 1968-1972 frame on a 1973 with the front inner horn change. No other modifications are required. There were 30,464 cars manufactured in 1973.
1974 - In 1974 the front inner horn was left the same as 1973 even though the front bumper extension changed. The 1974 frame rear section had two changes to it to accommodate a newly designed two-piece rear urethane bumper. And end section was added to the rear most cross member and a plate was added to the side of the frame for strength. An impact absorbing system was then attached to the frame and a rear impact bar was attached to that assembly.
Removing the rounded impact brackets makes this rear section the same as 1968-1972. The frame itself is in essence a 1973 frame with two brackets attached to it. You can use a 1974 frame on 68-73 cars with little modification. You cannot use 1968-1973 frames on a 1974 car without replacing the rear most section of the frame or you will lose your impact capabilities. There were 37,502 cars manufactured in 1974.
1975 - In 1975 they figured out a new and improved front extension system for the bumper and used the same front inner horn on the frame. No change up front. A new impact system was developed and deployed in the rear of the frame changing the rear significantly from earlier years frames. Significant change is required on a 1975 frame in the rear section to be able to use it with earlier year body styles. There were 38,465 cars manufactured in 1975.
1976 - No significant change from 1975. There were 46,558 cars manufactured in 1976.
