Well first off, it's a 40 year old design pushrod engine (basically), so don't get too worried about it. It's not like it's a new McLaren P1. That being said, Mobil 1 is a bargain these days. In the old days, stepping up to synthetic was a huge investment. Now you can get Mobil 1 for like $26 for 5 qts at Walmart, and I think the cheapest conventional is like $18 for the same quantity. Can't go wrong with Mobil 1.
Kurt