For what it's worth, the original Pontiac car distribution bulletin, sent to all Pontiac Dealers on February 7th, 1969, alerted the dealers that the new 1969 Trans Am would begin production approximately April 1st, 1969, and be built in the Norwood or Van Nuys plants. The bulletin lists the RPO codes that the Trans Am would consist of, along with items such as full length stripes, airfoil, Cameo white/blue stripes only, specific hood with longer scoops, etc.

The first two items listed are:

Code 348 - 400 HO engine (L-74)
Code 611 - Hood Ram Air Inlet (T-42)

Of course, we know the 69 Trans Am hood was unique, and did not have a flapper assembly like the standard Firebird Ram Air or RAIV hoods did, but this is what Pontiac called the Trans Am engine at that time.

I still like my theory that later in the year, Pontiac combined the "348" and "611" codes into "R/A" on the invoices.

If not, then the term "R/A" was used throughout the year, based on assembly plant, while "400HO" was used for other plants. Remember, "R/A" was used on GTO invoices to signal the Ram Air Engine (aka RAIII), so perhaps a Firebird assembly plant used "R/A" on their Firebird invoices in a similar way, whether it actually had the Ram Air hood or not.

The 1968 Ram Air models (Bird or GTO) used 3.90 or 4.33 gears, but this was not the case for 1969 Ram Air models. The 1969 Firebird 400HO, whether it had Ram Air or not, came standard with 3.55 gears, ditto for the 69 Trans Am. The RAIV's of course were standard with 3.90's, optional 4.33's. The same gear ratio options were used on the Ram Air GTO's and Judge's.