Ah, gotcha. I'm sure there's some major rework done. The Flight caption cheerily mentions that it only took "a matter of weeks", which—in fairness—I know isn't very long in a flight-capable experimental installation. Still, the fact that it's no longer pursued and was never selected over 20 years of marketing might suggest that it wasn't as straightforward as something like the F110 in the F-15 and F-16.
I recently read that the UK is looking at a AH-64E Guardian-style upgrade for their Apaches, but what they'd be doing with the engines and transmission was unknown (I imagine they'll be skipping that portion). Choosing to go with different systems than the US can cause complications with comprehensive upgrade programs and add expense, I know. It seems to be a lot more straightforward for other operators as long as they have the money.
Cheers,
Logan