Newest car I could spot was the '58 Olds near the front of the photo. I didn't notice any other '58s. Mostly'55 &'57 Chevys and '56 Fords. Odd it was hard to find any '56 Chevys.
Naw.... the cool guys with the '56 Chevs were all cruising Bob's Big Boy when this picture was taken!
That's looks like a Franklin 595 cube flat 12 aircraft engine. About 350 hp for reliability..but could make more power if falling out of the sky is not an issue.