There weren't too many '65 Pontiacs with 289s, if it was an Oshawa [Canadian] built GM, it would actually have been a chevrolet chassis [including drive train] with a Pontiac body
That car [base] would have had a 283 powerglide combination
If it was an American Pontiac, the base engine would have been a 389 2BBL with a three speed ST400 switch pitch automatic which was faster than the '66 Canadian 396 4BBL T400 [in the first couple blocks] but that's another story
Anyway, getting back to oil, when I got my XL600 it was a disaster the spacer plate and O Ring for the dual sequential carbs was blasted out and you could barely kick it over; gurgling and oil everywhere; in the airbox,
Got it home and checked the manual [I did... I do sometimes...

] said it takes 2.1 quarts
Drained the crankcase and oil reservoir - five litres and a bit was in there
Probably a fate that beset many of these bikes, The RFVC dry sump engines on these bikes have two oil pumps, one for scavenging and pumping back into the frame reservoir the other I'm not sure what it does
There's a dipstick at the top of the frame reservoir to indicate the level The only problem is that with many of these bikes, they only need to be a few years old and sit for any length of time before the check valve at the base of the reservoir either fails or never worked in the first place, and slowly passes the oil back into the [supposed to be] dry sump crankcase until the levels equalize
Rider comes along, does the right thing [wrong thing], checks the oil, tops it up before kicking it over, and over, and over...
Moral of the story, if it's low on oil start it up, let it run for a while then check the oil. Sounds like the script to one of the Rust Valley episodes