If the MAF is calibrated for 24# injectors and he has 24# injectors, the computer shouldn't have to adapt at all. His air/fuel ratio should be correct. The difference will occur at idle. I don't think it will, though, since the injectors probably can open and close fast enough. You'd start running into problems with 30#er or more. Just because the injectors are rated for 24#/hour, doesn't meant they will be putting out that much.
There's no basis for you to say that the computer can only adapt a little. The example in the book was that they set the fuel flow to the engine to run 20% rich and the computer adapted within an hour of normal driving. To put that into perspective, GTLee would have to lower his fuel pressure to 25psi to be 20% out of spec.
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351W 89 Mustang GT Convertible