The oval track springs are offered in thicker material than the stock springs sets, so that would explain the 3/8" thickness. The 20.5 front segment also point towards an oval track spring as A body and Super Stock springs are 20" and regular B/E springs are 22". Part numbers don't jive with oval track springs though, so maybe they are either an old set with a different numbering schema or from the original company making them up for Mopar. FWIW, current Mopar part numbers are P4529415 for 1" arch and P4529414 for zero arch.