Then you bolt on engines it was never designed to use. Congrats you've described the overwhelming majority of 737s ever built, as only the first 1,100 or so (a

Then you bolt on engines it was never designed to use. Congrats you've described the overwhelming majority of 737s ever built, as only the first 1,100 or so (around 9% to date) were built with the JT8D. Or you've described none of the 737s ever built if you consider that any airliner was designed for whatever engines it was installed with.