That's a category which has a secondary metering plate (instead of the 4150 with a block with jets and dual floats), in many sizes, not the list number.
Common 390 list numbers:
8007 with .038" PVCR (common for L6 and small V8)
6390 with .031" PVCR
R6299-1 with .021" PVCR (for L4 engines)
Remember that the size shown supplies fuel at WOT proportionate to the square of the ID: the .038" is 150% as large as the .031" and 300% as large as the .021".
The final WOT fuel is the total of main jet + PVCR. If you increase main jet to size to compensate for a small PVCR, your gas mileage goes away.
