Rocky, just to confirm, are you saying that no base '73 Trans Am (standard L75) got the M20 and no '73 Formula with the L75 could be had with the M20?
Do you know if a later revised version of the '73 Firebird Order Form exists, the one I have is revised 6-12-72? Perhaps the trans option choices were corrected at some later date?
I am convinced that the M21 could be had in the TA and Formula with the L75, but trying to determine if the M20 was possible for either or both.
The Accessorizer clearly states that the M20 was Standard for the Trans Am. And the early Order Form not only implies that, it also shows the M21 as Not Available for the TA. But no such prohibition was indicated for the Formula which doesn't seem at all logical.
The verbiage from the Service Manual excerpt seems to align with what you and HFR have indicated, that is, the M20 was available for the 4 bbl 400, an engine that was only offered with the Formula.
And the M21 was ALSO offered for the 4 bbl 400, a choice that seemingly was readily made on the Order Form. But the only 4 spd allowed for the L75 according to the Service Manual description was the M21.
If the Service Manual was correct and the evidence seems to agree, the Order Form and Accessorizer were wrong. That would not be earth-shaking news.
The Service Manual and the Order Form would both seem to suggest the 4 bbl 400 (Formula 400) could be had with the M20 or the M21 as a buyer's choice, no other ordering restrictions seem likely and you have found no evidence to suggest otherwise.
And while the Order Form did not indicate a prohibition for ordering the M20 with the L75, perhaps any such attempt to order it that way was over-ridden at order entry.
My early GTO experience makes all of this a bit strange to me. When the M21 was made available very late year for the '64 and continued for the '65 GTO, you could only get it with the 3.90 axle among other mandatory options (was not required with the 3.90 but couldn't be had with lower numeric gear ratios).
But for the '73 Firebird, they were allowing the M21 with some pretty low numeric gear ratios although I am not certain what ratios were available in the Formula or Trans Am.
And I also think it is bizarre that they put the M21 behind the D port 455 but put the M20 behind the 455 SD. Was that intentional to give the SD a "quickness" advantage? Or was it in recognition that the SD could stand higher revs than the D port 455?
HFR, do you have an Axle Ratio availability chart for '73? Was the 3.73 axle available? Were the axle ratio choices same for the D port 455 as for the SD?
The Order Form seems to suggest a G92 Performance Axle option was available for the Trans Am. Relying on my early GTO experience again, no performance or economy axle regular option was released for the '64 GTO, but it was possible to special order a limited variety of approved numeric axle ratios for the '64 GTO while other ratios were only available over the counter from the dealer. Curious if special order ratios were allowed for the '73 TA?
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