The "Sprint" suspension would have lighter front coil springs, a lesser drivetrain, and narrower tires. I see no advantage to the theory of "Sprint 400".

The only indication I have seen so far is on the 1969 Firebird order form, J50 power brakes, "N/A with 345-347-348". 347 is not separately enumerated as a powertrain option on the 1969 Firebird order form, but it IS listed on the 1969 Pontiac All Series Special Equipment Order sheet. Code 347, L67 Ram Air IV. FGF's own information states that for 1968, "Ram Air II production started May 20th 1968. The option code was still "347" however, the package price was increased. (sometimes found noted on the Billing History). " Interestingly, the "Ram Air" option is only mentioned once on the Firebird order sheet, code 611 "Hood Ram Air Inlet" optional on 348 only. 348 is the Firebird 400 H.O. The code 347 Ram Air package is not broken down by line item on the special order form.

As to whether the book (I'm guessing the Pete McCarthy book?) used the "addition" method to try to decipher powertrains, I can't answer that. It doesn't work with powertrains or transmissions as you cannot have more than one. Other options, like AM/FM stereo radio (388) with power antenna (381) may be shown as 389 (add the last digits 8 + 1), or may be listed separately as on my dealer invoice for my 'bird.

I was hoping the Firebird registry would make some of the code information public, but it appears that even after two years they've not gotten far enough to release it. I have roughed in the sheets for 67-69 and am populating them with the UPC and order codes directly off Pontiac order sheets. If anyone has an original, clearly legible copy of the '68 and '69 order sheets so that I can confirm the accuracy of my transcription of the microtype letters, please let me know!