This article was written by Chris Teeling.
Big block (390 & 428 CJ) Mustangs and Cougars produced after March 1968 were built with reinforced front shock towers. The reinforcements were added due to shock tower cracking issues that had resulted in warranty issues for Ford and Mercury after the introduction of the 390 engines in 1967.
The reinforcements are a key identifier for 1968 ½ Mustangs since the lack of the reinforcements indicate that a car has had major front end body work or that it is not an original 1968 ½ 428 CJ. The shock tower reinforcements were carried over into 1969 and 1970 model year big block cars and were even included on 1969 and later 351 powered Cougars.
The reinforcements consisted of 3/16 in thick (7 gauge) carbon steel plates stamped to conform to the inside profile of the Mustang shock towers. During vehicle assembly, the reinforcements were spot welded to the shock towers in order to provide better support for the increased engine weight and loads transmitted from the engine mounts in big block Mustangs.
The reinforcement plates were changed each model year during 428 CJ production although the introduction of the changes may not exactly align with the model year introduction.
1968 ½ 428 CJ Mustang shock tower reinforcements (images courtesy of Chris Teeling):
For the 1969 model year, both sides of the reinforcing plates were made a bit taller and the shapes were simplified.
The reinforcing plates were changed again for the 1970 model year with the tops being made more angled and a notch added to the driver side front and the passenger side rear (images courtesy of Norm Collamati):
Comparison of 1969 and 1970 reinforcement plate details:
1970 reinforcing plate notch location: