Either 2 or 3 will be for the throttle linkage, depending on the year of the vehicle, and possibly the vehicle the engine is installed into. Yes, the hole near the oil pan rail is for the return line from the bottom fitting of the oil filter.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!