How many quarts of oil and what kind of oil

GM 305 engines typically use 5 quarts. Try that and, when done, see how far up the dip stick the oil marks. If it shows "full", leave it alone If it shows low then add more until it hits full Probably another quart but add it about a quarter of a quart at a time. Allow a minute or so between adding slugs of oil to allow it to flow down into the sump at the bottom of the engine.

5W30 ought to do it. If it uses oil try 10W40 or 20W50.