Correct. And the spacing of the studs that hold the barrel to the cases is different too.
You can fit YZ-D/E top ends, along with monoshock DT125/175 top ends, or IT175 before 1980. Or IT125.
The earlier YZ and the DT parts will both require a different exhaust pipe (or mods to make the F pipe fit).
IT125 barrell will take an unmodified F pipe.
Not sure about IT175 bits (but I think they require mods).
Apparently a YZ125E top end and pipe is the hot set-up to avoid the peakiness of the standard F.