My truck has (F453 30 1023) on the ID tag in the driver door jamb. I've never seen a letter after the initial series no. ie: 452 except once, & it was a "x" after (HF 602x 31 1245) This was a 600 series "Cannonball" COE I once owned, & the "x" in the ID number denoted it being a special order wheelbase. Your "a" has me puzzeled. I saw a air over hydraulic '54 GMC 450 series once with "Hyd./Air" on the glove box lid plate, nest to serv. brakes.
