Hello, would there be some good current options for recommended oil for 1975 Eldorado 500 CID GM engine? Mileage is at 50K (original!). Owners manual just says "good quality SAE 30". I wondered with all the improvements in motor oils since 1975 if there would be a benefit to using a particular type in that BIG engine. Also, oil filters sold to fit this vehicle seem to be very small in size and overall filter area. Would not that effect ability to filter adequately? Thank you in advance for your replies. Ttommy.