The 75 pontiac service manual says for V8s (doesn't say which ones so I assume all): If you change just the oil and not the filter you need 5 US Qts. If you change both the oil and filter you need 6 US Qts. However this obviously assumes your filter will hold 1 US Qt. I'm using a PH25 on my 76 400. It will not hold a full US Qt. So changing the oil and filter requires about 5.5 US Qts, maybe a bit more. I expect 6 US qts will a bit overfilled. Too much overfilled? Don't know. There is 4 - 5 inches from the filter to the exhaust so you could put on a filter that holds a US Qt in which case you will need 6 US Qts.
