A53 is the SCCA Trans-Am homologation package — Chrysler's 1970-only Sport Package built specifically to put the Plymouth AAR 'Cuda and Dodge Challenger T/A on the road in legal-for-sale form so the racing program could enter the SCCA Trans-Am series. The road cars displaced 340 cubic inches (the spec-class limit) and ran the 340 Six-Barrel intake — three Holley two-barrels on a long-runner aluminium intake — making about 290 hp gross and 345 lb-ft on regular pump gas with 10.5:1 compression.
Every genuine AAR / T/A carries A53 on the fender tag, AND the J-code engine character in the VIN's 5th position, AND an M0-prefix sequential build number (the Hamtramck plant's homologation overlay). Any one missing is a red flag: A53 without J means the engine was swapped (or the tag is fake); J without A53 means the package was deleted post-build (rare and usually obvious from missing hardware); A53 + J without M0-prefix means the car was built outside the Hamtramck homologation run. Plenum surfaces all three signals on the result page.
Build totals: about 2,724 AAR 'Cuda hardtops + about 2,539 T/A Challenger hardtops produced for the 1970 model year only. After the 1970 SCCA season the racing program was suspended and the package was dropped; A53 never appeared again. The road cars are the surviving artifact.