Yes, the 76 CB550 carbs have the clips. They are on the slide needles. The slides must be removed through the tops of the carbs to readjust the needle depth by repositioning the clips. There are also needles with different taper profiles (F model Carbs) to change mixtures at certain midrange throttle settings.
Be prepared to resynch the carbs with manometers after slide reinstallation.
Minor point. Your main jets aren't really press in, as that implies the retention method. Your carbs have spring clips that hold in the mains.
If you've done a plug chop at WOT, and your plugs have white or no deposits on the center electrode insulator, you may need larger mains. There are jet reamers and guages available to make yours larger.
