I use Quaker State 10W30 in my 49 (56-235) and in my 81 Malibu. I have 500,000 kilometres on the Malibu and have not opened the engine. I have changed the stem seals only. I change the oil in my 49 every 1000 miles (paranoia?) and every 2000 kilomtres in the Malibu.
Doesn't mean its correct, just what I've been doing.
